Live streaming a sporting event - how to do it?

Hello - I organize running races and this year I'd like to set up a laptop at my finish line and stream the finishers coming in through the race Web site (through ustream or justintv for example). I'm not sure how quite to do this without an internet cable or wifi nearby. I imagine I'd need to tether the laptop (PC probably) to a phone with a data plan (plenty of friends with iPhones). Any suggestions?

thanks. -c