I come from a family with a lot of manic depressives, bipolars, and other such ailments. Genetics, family histories and tendencies, lots of different reasons for it.

What I've found is that with people as painfully socially awkward as these is that they need to somehow find something, anything, to be interested in as a starting point in social recovery. Sports, videogames, comic books, music, whatever. Just something to get excited about. It sounds, from your descriptions of him, that he doesn't have much in the way of these kinds of hobbies or interests and thus no outlet into any type of social network.

I'm not normally a proponent of online gaming ala WOW, but maybe something like that would benefit a guy like your cuz. At least it's some sort of interaction, without the pressure of face to face communication. It's a starting point, at least. Wish him the best.