I think that srunni's answer is probably a good start, but I'd also add another approach. Until recently, the Wash U CS program was run with a heavy focus toward academics rather than industry. As a result, most of the really talented students weren't really going to career fairs, they were instead looking for interesting research positions. It's possible that things have changed since I left (there's a new dean and department head), but I'd guess it's still about the same.

If that's the case, you really need a way to reach those top tier students. Do you have any positions that would seem intellectually rigorous and interesting? If so, I'd find a professor with relevant interests and shoot them an email saying you're looking for a top-tier intern and that you have some really cool problems for them to work on. Some professors are obviously more industry-friendly than others, but in my experience, there are at least a few who would probably be willing to help.

Another option would be to host an event at Wash U. I'm not entirely sure how this works from a logistical standpoint, but it's common at Wash U for companies to reserve rooms for different types of recruiting events. Some companies might host hack-a-thons. Some might do giveaways. EA did a presentation on how video games get made. Those events generally get a lot more attention from the top tier students than the career fair booths, and professors often promote them at the end of class. I'd guess that contacting the Career Center would be your first step if you want to set something like that up.

Hope that helps.