I would also recommend getting there a bit early. Before the show, there are "Jedi assistants" who come and chat with people. He should try to carry on a bit of a conversation with them. And, if you get there early, you will be in the front, which is good for visibility. Then, when the Jedi Master comes out, he should be enthusiastic (arm waving, calm jumping) when they start picking. And yes, in our experience, Star Wars clothing did appear to help.