Check this out.
http://www.paysitepowertools.com/os-multimodauth.html
This guy posts on here, but doesn't seem to push his software. It seems like a valid solution, although the price sucks ass. On the other hand, anyone using referrer based protection knows what a PITA it can be. Especially with surfers who's ISP blocks referral headers. ;) So the price may be reasonable if your have enough bitchy members, and referral spoofers.