Whatever you do, make sure you go out and talk to him. Having been that kid who's outcasted, nothing hurts more than walking away because you weren't accepted, and having no one stop you from leaving. So whatever you do, include him in any way possible, like maybe ask him for ideas on things you're working on for the team. If he can't be officially on the team, bring him in in any way you can find. And good job for being the one with guts enough to include those that don't always agree.