So you have mentioned a lot of things that make him angry and frustrated. Can you think of one thing that he still has a spark for? Can you think of a way to feed that one thing, without him thinking you are "pushing" him? What is his primary mode of learning (visual, auditory, kinesthetic)? Can you let him indulge that mode of learning when he is home?
I have been fortunate to not have to face this as a parent, but I had a HG sibling (who was very kinesthetic) who hated everything at school, but loved helping his dad in the family business. The knowledge that he would get to come home and take equipment apart kept him sane and engaged.
