I don't know your son's abilities, but did you think about a heavy cross sticks or chunk type gun that you could shoot from a rest and its mass would absorb the recoil. If your son could hold the butt in his left hand and pull the trigger with his right, leaning into the gun then he could have the experience of shooting the gun by himself. You could even possibly have a harness that holds the butt to his shoulder and set triggers would make the trigger pull easier. Just a thought. I am building myself a chunk gun because of my physical limitations, and I have been in a wheel chair before, paralyzed from the chest down.