I had a few disabled students over the years. One young fellow comes to mind. He and his sister both had some kind of muscle disease. He wore leg braces, could walk but it was quite an effort for him. He was around 10 years old. He trained with us for 2-3 years. For a long time I put someone behind him when we did the exercises, without help he would fall down. He actually had to be held back, he wanted to do much more than he was able to do. We just worked with him along with the other students and his physical condition actually began to improve. Eventually he was able to take off his leg braces. His doctor and his father were amazed. I do not know any plan or books that may help you. I suggest you just work with your guy, let him do what he can do and adapt where necessary. Maybe his physical condition will improve, maybe not. But as long as he is happy and keeps himself busy, you will have the satisfaction that comes from helping him do what he wants to do. Good luck!