Can Mountain Lion bridge two network adapters for Parallels VM use? I need bridged networking under Parallels for a VPN from the Windows VM. However, this conflicts with my main OS (Mountain Lion) using the same adapter. I'd be happy to direct the mac to wifi (AirPort) and the VM to Ethernet, but how do I do that?
I know this option probably isn't convenient enough, but if this is a deal-breaker problem…

You might consider switching your VM host software to Fusion, which supports this (and is somewhat more advanced than Parallels generally) use case natively.  The Network Adapter control panel in VMWare Fusion: