Two Public IP's one system

I have asked about this before but I think I can ask more intelligently now.

My PBX is behind a firewall but I have customers accessing the system via static IP address from the outside. So they use NAT. I have the extenal IP set and localnet set to my ip addresses.

Here is where the problem comes in. My SIP provider gives me a public IP for accessing my sip trunks. I can’t use this WAN for anything but accessing these sip trunks. Everything else is blocked. Also I can access my trunks only via WAN.

I have to attach the SIP Trunk WAN directly to the system via a second network interface. Then add the WAN ip as a localnet entry so it does not do NAT.

This works fine but now I am trying to set my system up on a KVM guest VM. I can’t put the IP on the system anymore as you can’t map a physical interface to a guest instance (as far as I can tell.).

So my question is, can i set the externip and localnet differently for a trunk then for the rest of the system? I need the system to use one externip and set of localnet networks and the trunk to have a different externIP and localnet settings.

My guess is this not possible… but i figured I would ask.