Scott...I know you are saying chair and aiming toward skateboarding and some air time. I'm trying to wrap my head around something light, agile, able to jump/get air in the type of situation you are describing and am having trouble. It did bring back some memories of going ATVing with a couple of guys who were paralyzed. At the time, there was no power steering on ATV's, now there is. Not sure where I'm heading with this.. thinking aloud though.

With his limited muscle mass, is he able to get moved around a decent amount w/o it draining or hurting him?

Guess I'm kinda thinking of starting with something along the lines of an ATV and building upon that. The cost is probably an issue as most of them aren't cheap. But it seems like a way to potentially bridge the gap of him doing stuff at a reasonable cost.