I'm not sure a frat-ish vibe is the best way to accomplish that, though. In particular, I don't think cultural geekness is the problem; women are fairly well represented in cultural geekdom outside of programming, especially in recent years. For example, most sci-fi/fantasy fanfic authors are female, and gender balances at general-geekness conventions (e.g. Comic Con) is closer to even than it is at specifically tech events.