Do you have a fan or air conditioning? Turn that on colder than usual (unless you fall asleep by that, in which case, turn it off). Drink cold water, and get up and stretch every once in a while.
Is there anything that needs organization? Folders on your computer, your sock drawer, your closet, CD collection? Go at it, with some music playing.
I've had to do this before, too, it's a pain. I try to keep from from staying in one position for long until I'm within 10 minutes of my sleep time, or I'll just fall asleep.