Sometimes giving the guest something different to talk about seems to get you more interaction with them and obviously also being lucky enough to be there at a time when they aren't dealing with an enormous queue. This worked with both William Shatner and Christopher Lloyd for me. Having a copy of Bill's new book for him to sign led to a short chat about the book and my thoughts on it. And a mention of Jim Ignatowski got a reaction and a handshake from Christopher. It probably made a change from questions on Star Trek or BTTF.