Oooo. Since OSU has that crazy 10-girl rule (
yup I'm familiar with it.) You could use the postive point system that allows girls to choose many different things.
For instance, take a look at your chapter programming and assign point values. Ritual is higher than a TG, etc. Also weight points based on past performance. If you notice you're not getting people to show up to Phil events then they get a higher point system.
THEN when sign-ups for the different parties happen, the person with the most points gets to sign up first for that party and so and so on.
That would be my first suggestion.
Second you could also use the point system for "get out of jail free card" type situations. I can't remember where you chapter stands among the other 13 on campus, but you could definately split up and give some people an off night. That break could be just the motivation they need to attend an event where PR is key.
I'd be happy to talk to you more about this - PM me and I'll give you my phone - since you're right here in C-bus.
Heidi