We recruit with duct tape & zip ties. Grab them when they're not looking, zip tie their limbs together and keep them still (and quiet) with duct tape. When they agree to join the team, we set them free. 
ahem.
Start with FLL in elementary school, move up to FTC in middle school. By mentoring these teams in our sending districts, we have a built-in stream of interested freshmen each year. In fact, some think our team is too large.