I do think you need to start further up in your hiring funnel than the phone screen: were I in your shoes, I'd be trying to get more minorities to submit resumes in the first place. One of the problems identified by those studying diversity in tech is a self-selection bias: minorities, and women especially, seem to send out fewer resumes and less ambitious about the positions they apply to. Perhaps consider reaching out to groups like RailsBridge, Python Boston, PyLadies, Ladies Learning Code, etc., and letting them know you're hiring and want to talk to candidates from their communities? Drop me an email (and let me know where you're located) if you'd like me to try to help make you some connections.
Re-reading the above, I'm hoping it doesn't come across as critical; it's clear you're taking this very seriously, and that's awesome. Just hoping I can help more!
There's a local hackerspace that has women groups, I think. I'll start there. Thanks for the advice!
I actively pursued an acquaintance of mine to try and get her to work for us, as she was just graduating from a top engineering undergraduate school and was an actuary. Sadly, she took a position in NYC (understandable).
We're very strict on hiring, so we do interview many candidates for each position that opens up (we have plenty of open positions now that we can't seem to fill).
If we set an interviewing quota, it could literally take us years to hire someone for a mid-level developer position simply because we would get no applicants or no referrals from recruiters that were women. It's just how it is. Very sad.