I did not find a way in stock * to do this. The Alert-Info header field on incoming calls is not parsed out.
So I created a patch to set the ALERT_INFO variable to whatever the Alert-Info header says. I can now handle the Broadvoice primary number one way, and the alias another.
This is my first * hack, and since I am not familiar with the architecture there may be a better way to do it, but here it goes: