You're all evil, and I hate you.
That being said, this should still work.
You have 2 routers. A and B.
Router A has WAN2 connected to LAN2 of Router B
Router B has WAN2 connected to LAN2 of Router A
Router A has LAN IP address of 10.0.1.1/24
Router B has LAN IP address of 10.0.0.1/24 (this is important, LAN subnets must differ for this to work correctly)
Router A's WAN2 configuration could then be:
IP: 10.0.0.10
Subnet: 255.255.255.0
GW: 10.0.0.1
Router B's WAN 2 configuration would then be:
IP: 10.0.1.10
Subnet: 255.255.255.0
GW: 10.0.1.1
(note that WAN IP addresses are opposite from those of LAN IP's).
The final step in this configuration would be to configure the WAN Load Balance Policy on both routers to have:
Source: Any
Destination: Any
Service Type: Any
Binding interface WAN1
Failover to other WAN: enabled
In this scenario if the primary WAN of either router were to fail then the traffic would fail over to the other routers connection. You would still run into a 'double NAT' scenario... but as this setup would be an emergency measure this should not be too much of a concern.
