How about a subscription to a magazine so he can lock himself in his room
RC mag of course
When I was that age i wanted to get out more, maybe organise a camping, fishing, hunting or road trip.
Get him interested in money and say you've got some money to invest in shares. It's his money then so he'll want to study up and not lose it. 'Blue chip shares' are reasonably safe but this idea may not be profitable enough to be interesting.
Something that requires a portion of responsibility. Like a dog but at that age he might be over the pet thing.
Just read OP so I guess the road trip is out. Is he interested in water sports, a new wake board? Or a joy flight in an ultralight? Bungee jumping or skydive? Joy ride in a rally car?
I know there's nothing here that can be related to school in any way but I was farily uninterested in school.