How do you put an adult diaper on someone who cannot stand or roll over?

That's a tough one, although logic tells me there must be a way because people with spinal fractures would have difficulty as well. Do you have the help of a hospice provider? Would you consider using a lift?
Another thought, using a catheter for urine would help cut down on the number of changes.

I have used a lift for my dad, and it requires shoving the canopy under the patient - for which we used the roll over method, same as you described. The catch here is the inability to breathe on his side. I do not know if ther is one that can just pull him up by the shoulders. Short of mechanical help, since he is no longer able to stand - he may need to be held vertically. No doubt this is not a one person job.
If you are trying to care for him at home, it may be time for a facility hospice, were there would be sufficient staff to attend as mother nature calls. The catheter suggestion is very good as well - all this jarring must be very uncomfortable to the patient.

Best of luck

Maybe a thick foam square to lift the legs enough to clean him up. Then two diapers at once so that when one is pulled out, the other is still in place. I haven't tried it myself, yet. He should be moved occasionally to prevent bed sores so maybe lifting his legs will help with that too.

Using the rolling technique, your father shouldn't be on his side for long enough to trouble his breathing - it's only a brief moment just while you position the diaper under his hips. Do you have a slide sheet? Are you doing this single-handed, or with another person?

The only other thing I can suggest is using bed-pans and bottles on a fixed schedule, and plenty of absorbent pads on the bed; but obviously that will only work if your father retains any sense of urgency when he needs to go.

Do you have a hospital bed for your father, so that you can change his lying position easily?

I found straps that go on the leg. Called Lavin Lift Straps.
They go around each thigh and have loops on the top. The loops are then attached to a Hoyer Lift. the Hoyer is then raised and that raises the lower half of the body. I found that raising my husbands legs while lowering the bed a bit gave me enough room to pretty quickly change him.
There is a Youtube video that demonstrates how they work. I purchased the straps through Amazon as it was a little less expensive than other places that had them.
Hope this helps.

My husband, (stroke patient) has used a condom catheter, at night. This has been a life saver for us. Though it won't help with bowel movements, it lessens the need for changing.

My MIL had COPD and Emphysema. When she was lying in bed I would roll her on to her side and hold her with one hand and position the diaper with the other hand. She was on her side for just a few seconds. Also she got one bedsore and I knew I needed to do something different for her cause this was painful. I purchased a Airone Alternating Pressure Pad. It was very quiet and and blew up different parts of the mattress so gently that she didn't even notice it. We had no more bedsores. This was only around $80 and was so worth the money.

We were just going through the same thing with our mother who has lung cancer which metastasized to her adrenal glands, pancreas and brain. Our hospice nurse had us lay our mother on the bed with disposable pads horizontally underneath her bottom and then to lay a 'tabbed' diaper covering the front of her while trying to tuck the back portion under her genital area and legs (not too much that it was uncomfortable for her). Then when she would soil them, we'd still need to roll her to one side while (a) rolling up the soiled towards her and rolling out a new one, then (b) rolling her to the other side while rolling up the rest of the soiled one and then the new one. It helps if they can hold onto a bed rail (if you don't have side bed rails, try to get one (hospice can provide if you are receiving their services). Then wipe and clean.
I understand that he still won't be able to breathe when he is on his side, but hopefully this is a quicker method. You could also consider a catheter, which would make all of the above a moot point.

Are you using the briefs with the tape on them, if not you should. Your letter reads as if you are trying to get the pull up diapers on him. With him lying on his back,fold the diaper over your hand and just push it under him and tape it on the sides, no need to move him onto his side.

I agree with virginia55 using the large tape fastener diapers are on call here. When you change his bed, what do you do? You can put the the sheet, the bed pad, and the diaper in place at the same time. If there's someone there to help you that would be a big help! Having someone to help would make it easier on your father. When you only have to change his diaper If someone can push down on the mattress while you slide the diaper under your father, that's worth a try also. My prayers for your father and you, we all know it's difficult, from experience I'm thankful I was able to take care of my mom at home before she passed away.

I agree with the tabbed diaper. I was using the pull-up type on my husband, and when he went to rehab, the STNA changed him once in my presence and I watched and learned. She did it exactly as described above. Not only that, but she said the elastic in the pull-up was irritating the creases of his skin. When he returns home, I plan to use the tabbed diapers. Much easier!

My husband is a paraplegic. I use Depends Adjustable underwear. I tear the sides on the perforation and then use the adhesive strips to close. I roll him over once to position and adjust the diaper to fit. I find that this brand and type works better for us then the diapers with all the plastic.
Maybe this will work for you.

But the adult briefs that snap on the sides. Roll the diapers. Then roll them under him and them snap them under him. Like a small baby.

You could try using a bed as the changing table and just roll him onto the diaper, and just put it on him if it's one of the adjustables. If it's a pull-up, you can still have him laying down and just pull it up as far as his knees and have him pull it up when he stands up to transfer to a chair. if he's able to actually set up, you can even do it with him sitting. If you need help, I would just hire in home health to do what you can't 

I agree with trying the various methods discussed here in the responses. I'll add that we left the Hoyer sling under my mom at all times and put the pad and everything on top of the sling so we didn't have that step of pulling it out from under her each time. Mom screamed every time I changed her because of the pain but it had to be done and I cried every time. I also lifted her legs up (like I was changing a baby) some of the time. It was a little harder on me but easier on her and if she had lived longer, I would have used the Hoyer to lift her legs up. Mom also had COPD and yes, it's tough - this part was worse than any other part of caregiving because of what it did to both of us. It hurt her physically and broken my heart. I only had to deal with the diapers about a week before she died. She was still able to stand until that last week Then she just started crumbling in a heap and at 200 lbs, I couldn't hold up the dead weight, even with help.

They do make standing lifts but they're expensive - you have to buy them outright unless you are in Canada. They aren't supplied by anyone in the USA.

This may not sound like any genius idea, but you get a bedside commode, put him on it, then place the diaper around his legs and pull up.

I found that using the foam triangle pad to support the patient on their side to change them, wipe them off worked well.
If you can't find the side tape adult pants, then get the regular ones and slit the side and use a carpet tape or duct tape or even packing tape to secure them. Also use a separate super absorbent liner pad inside the pants, it can be peeled out and replaced inside the pantie if the pantie itself did not get wet. This is also a cost effective option if you are going through a lot of panty changes each day.
One caretaker on a tight budget buys the panties, and a lot of the super absorbent liners. She put some plastic wrap in the absorbent part of the panty, then adhered the super absorbent liner to the plastic wrap, then tucked the plastic wrap through the leg openings to secure it in the proper place, so when her bedridden mom needed a quick change she slid the panties down pulled out the saran wrap and pad and replaced with fresh.
Any BM always got a complete fresh panty and liner etc, but this worked well for urine situations which were very frequent for her mom and very expensive in the cost of panties. (she has since added Ditropan (oxybutin) to her mom's daily medications which has reduced the number of urination incidents each day. She went from 8 to 10 changes a day to 4 or 5 a day.

I understand putting on the tabbed diaper onto someone that's clean. But how do you clean under there if they are already soiled without rolling or lifting them?

You say he can't stand but can he weight bare while holding onto a bar. If he has strength in the arms, this method can be used but only if he is balanced while holding on. Does he sit in a chair during day? If so have a tapped pad positioned in the chair before sitting him on it. Try to position him so pad is equally distributed to front & back. Tape in best way possible.
If you have to change him in bed, use a slip sheet under the pad to apply as quickly as possible. As a nurse, I found this to be the quickest. Have two slip sheets incase one gets soiled. It won't kill him to roll over for a short time. It is more the fear/ panic that affects them when rolling. Stay calm or he will feed off your fear.
I agree a bedrail would help him to feel more secure as he pulls himself over to help ( if able)