Aw. You should just do it casually. Pretend he's just another one of your friends. Just bring it up, ask him if he's ever been. Maybe talk about it a little if he asks, then just say, "You should come." or you know... "Do you wanna come with?"
If he says no, then don't feel too bad. D: Don't worry!
If he says no, then don't feel too bad. D: Don't worry!