I would say don’t do it at the Q&A. He generally has a rule against that anyway because he doesn’t want to hug 850 people and a Q&A is supposed to be for everyone. If you can get a photo op, he’ll do damnear anything, otherwise your best bet is probably a handshake at the autograph table.
That said, John is an awesome person and he’ll certainly listen to you at the autograph table, just remember that there a lot of other people behind you that also want a minute of his time.
Have fun and let me know how it goes!