How do you sneak a photo at a meet and greet?

Next week I am going to a meet and greet where I will be meeting Alex Pettyfer and Dianna Argon. I will be meeting them at a local Hot Topic. They said pictures weren't allowed, but do you think there is a way I could sneak a photo with them? Mostly Alex Pettyfer. After the meet and greet we get a private screening of their new movie I Am Number Four. If they're watching the movie with us do you think they will allow photos? I just really want a picture with Alex Pettyfer. Is that even possible? :(