I have a Pix 515 at one site that I need to set up with P2P VPN access to another site. My problem is that the outside interface of the Pix is not an external IP address. The border router that I have at the location has two separate internet T1s coming into it from two separate ISPs. So connection between the border router and the Pix is a 172.16.x.x/30 and we route all traffic down that, then we use route mapping to force specific traffic down one of the internet pipes based on the source IP (using NAT).

Since the firewall's ouside interface is a 172.16.x.x/30 address instead of a real world external IP how do I set it up for the P2P VPN?