Ad Network by demographic/interest

I run a social network for college students. We have one Google Adsense ad (250x250) in a prominent location on the site but the returns are pretty bad - $0.35 eCPM. The reason is because we’ve been pegged as an education site by Google and are shown University of Phoenix and “earn your high school diploma” ads, none of which are helpful to users already enrolled in a 4-year institution.

I’ve done a good bit of research and it doesn’t look like we have much say over what category of ads Google displays. Obviously it would be much more effective if we could show our users ads for spring break, poker, posters, and other stuff college kids are generally interested in.

We’ve tried applying to some of the well-known networks (Casale, Valueclick, Burst), but have been mostly rejected for not having enough impressions/uniques per month (300,000/6,500).

Does anyone know of any networks for small to mid-size sites that will allow us to target ads by demographic/interest or can maybe just help point us in the right direction?