Relay? More electronics help here...

Okay, the mind here is floating back to the Woot!-Off lights and my idea of getting them to automatically light up whenever there is a Woot!-Off.  The lights are fairly simple -- they're a stationary LED with a motor that drives the directional reflector cones.  Repairing one of them was a easy resoldering job.  They're powered by USB, so we can assume 5V .5A max usage.

Now, I think to trigger it, I need a relay, something I can power at below five volts... any ideas?