Why limit it? Collect all relevant info (like college) as fielded data and allow employers to create whatever filters they want to focus on the type of employee they want.
If the employer got his/her degree from Cornell (for example), he/she might not be too thrilled to find that you've decided that job applicants from Cornell aren't even worth letting into the system.
Their value proposition is that you don't know how to identify the best candidates but you can outsource the problem to Developer Auction, which applies arbitrary criteria for you because as they admit, they also don't know.
If the employer got his/her degree from Cornell (for example), he/she might not be too thrilled to find that you've decided that job applicants from Cornell aren't even worth letting into the system.