Never mind... it's SUPER-easy to get this working without a UDID.
All you do is install iOS 5.1.1 clean... then activate your iPhone (setting up as new). Then.... very quickly... manually select the iPhone 6 beta build in iTunes by using the UPGRADE option (NOT the restore option) and update the phone. Because the phone was just recently activated and verified by Apple, and because the update is so fast, iOS doesn't check for verification again and the phone is fully activated in iOS 6 beta when the update is complete!