Maybe have one of the biggest fraternities or two host this in their parking lot/yard? I'd be willing to bet at least one of them would gladly put enough together to make it legit by their bylaws and such. I'm pretty sure they have a system with wristbands and can keep track of underage drinking as well as a bar could at registered parties. Probably would have resources to throw stuff together (speakers, stage, etc.) on short notice, too. Should be decent weather Saturday night, and warm enough outside especially if the place is packed. Just off the top of my head, DTD & AGR have a good space between their lots together, Pike has a big lot, and there is a pretty big space between Fiji, FH & Phi Psi.