Do they want to build at all? If yes, assign them student mentors, to the specific Sub team of ther choice (Electrical, Programming, Pneumatics, drive train, drive team, etc) if they just want to do something else then, how about chairman's team? Multimedia? Business? (fund raising) hmm, and you could always have team members organizing the food during long build days? The Multimedia team would be students designing shirts, buttons, and stuff for handing out at competitions etc..
