Good luck with your teenage stepson. I've teenaged daughters (one going into her 3d year of college, the other into her 3d year of high school) and getting them to do anything they don't want to (such as clean their rooms) is highly non-trivial. Getting them to do something they do want to do is less difficult, but still causes me to (figuratively) pound my head against the wall.

If you really think this is a path he'd be interested in, my suggestion would be to hire him, as your assistant in the volunteer project you've just started, or to write a database to maintain the inventory of the family collection of 3d dynasty palimpsets, or whatever. It's just got to be the right size for him to feel like he's actually doing something, and simple enough so he doesn't decide that he really wants to become a professional medical research subject instead of a CS major.