Maybe sewing the pockets shut. Rmove the linings. This might have something to do with tactile sensitivity. Maybe try a heavy sweater instead? Maybe give him some large beads to pop together, or puzzles to occupy his hands. Hope this helps. Hugs
My husband doesn't like material touching his throat so he cut off the top of the majority of his t-shirts. In his case devestatedinco is right about tactile sensitivity.