I ran across this great photobooth accessory:
http://www.shoplocal.com/dl-66135-digital-concepts-ac-adaptor-for-canon-s30-s40.fp
It says the Ac adapter is for Canon s30/s40 cameras but it works great with the canon power shot cameras as well. In addition if you are good at electronics you could wire this up to power a hot shoe flash like the Canon 550ex or 580ex flash by using a quantum battery pack adapter for around $6 at www.keh.com.
Of course you can always get your photo booth rental from us if you find messing around with electronics to be a shocking experience.