1. Make a "dummy" vlan.
2. Assign vlan membership to the port of your choice.
3. Assign Vlan id to the preferred port with untagged packet type.
1. Enter the IP address you want to pass.
2. Set network mask, 32 bits if you are passing only 1 IP address.
3. Set Interface responding to arp as WAN.
4. Set the Gateway IP address.
5. Vlan should be the dummy vlan that was created and assigned to your pass through port.