I don't think it's a horrible offense to respectfully approach a celebrity and ask for an autograph or that they pose for a photo. I'm sure Gamboa wouldn't interrupt him while he was on camera or busy. These sorts of shoots always have periods of downtime, and being greeted by a fan is often a pleasant distraction. You need to pull that bug out of your ass, DP.
Also... if you would be so kind as to try the sign Gamboa, it's very helpful to print out a couple pics of some previous sign holders... it puts the celebrity at ease. Seeing people like Ken Colley and Caroline Blakiston, who are respected thespians, assures an actor that they're not being set up for a lawsuit.