How do I give someone the light?

I have a question for all you comedy hosts out there: What's the best way to give someone the light? As you may know, I run the reading series In The Flesh, where readers have 10 minutes to read. I've had comedian Dan Allen on and on November 15th am hosting Comic Sex Night with Sara Jo Allocco, Claudia Cogan, Jessica Delfino, Todd Levin, Mindy Raf, Baron Vaughn and music by Adira Amram, but those aren't the people I'm worried about. No. Despite sending emails saying YOU HAVE A MAXIMUM OF TEN MINUTES TO READ and threatening to cut them off, people still tend to go way over their time limit, which sucks cause then I have to hurry along the later people. It's different than comedy in that you don't want to break the flow of a hot story, whereas if someone's telling short 1-2 minute jokes, there's more of a natural pause. But still, I have no experience with this and my natural inclination is to defer to the reader and be polite BUT that ultimately winds up screwing with my timetable.

So, I ask you for your expertise - what's the best, least disruptive way to give someone the light? Thank you!