I love memory foam. In England we have a place that you phone and give your specifications. They cut out any size or thickness MF. You could always get a piece from somewhere and cut an indent (where the ear would be) Thus no pressure on the ear (smiley face)
They do sell - as cwillie said - original ear pressure sore pillows, but they are expensive.
I asked this question a few years ago and sad to say there aren't any perfect solutions but I can tell you that since mom is in the nursing home she doesn't have sores on her ears because they don't allow her to always sleep on her right side, they are turning her often and she is frequently on her back. They do make special pillows for this with a hole for the ear, try googling "ear pressure sore pillow".
They do sell - as cwillie said - original ear pressure sore pillows, but they are expensive.
Good Luck