Do you have assigned 2 public IPs (IP0 and IP1) to the same ethernet interface of the Zeroshell router in the server side?
If so, don’t worry if VPN servers listen to both IP, you just have to balance the traffic in the client site:
1) configure VPN00 with Remote Host IP0;
2) configure VPN01 with Remote Host IP1;
3) add a static route for the IP0 to use the ADSL0;
4) add a static route for the IP0 to use the ADSL1.
At this point, VPN00 should use the ADSL0 and VPN01 the line ADSL01.
In the release 1.0.beta6 the Net Balancer will allow to make routing decision based on the tcp/udp port. In that case you don’t need to use two IP addresses in the server site.