I also went to UofH. It's probably not as bad as most commuter-oriented schools since it has a TON of student housing, especially now, plus there is Greek Row now, which throws a whole other dynamic in!
We had greek life booths at Cougar Preview, Orientation, etc. Plus as ajuhdg said, we passed out water and lemonade (along with rush applications!) at the dorms for move in day (this only works if there ARE dorms). When I was VP of Panhel, we had professional information pamphlets made with pics of the sororities and general info, plus a rush interest card that the girls could fill out and give to us. Also, the sororities were allowed to pass out apps to girls at the University Center, another place to eat called the Satellite, some of the major buildings of classes, etc. Once, we even got a phone list and called female freshman names!!! (this is panhellenic here...not specific sororities).
I was like a vulture when I was a rho chi. I went to every single orientation activities mart and I accosted every single girl I saw with a rush booklet!!!!! It was a cool challenge
Our school is also big about painting your car before and during rush with sorority messages. We painted the fraternity guys' cars too at their houses! Anything and everything to get the word out.
We had banners on campus for each sorority and the rush/greek life office phone number on them.
We had bright red GO GREEK shirts that everyone was supposed to wear on a certain day to make our presence known, while on the other days, the sororities had their own "shirt schedule" (at least mine did).
Basically, you have to make it IMPOSSIBLE that a girl could go to your school and NOT know about rush. It's still hard, I know, but it must be done!