The other thing you might be able to do is to set up the 615 router as an access point instead.
1) Assign static (fixed) IP to the 615 -- must not be the same as the 2Wire and must be outside of the DHCP range of the 2Wire
2) Turn off the DHCP service on the 615
3) Leave the WAN port empty on the 615
4) Connect a Ethernet wire from the 2Wire "LAN" port to a LAN port of the 615
5) Turn off wireless on the 2Wire
6) Set up wireless on the 615
After this all the "firewall" / port forwarding / virtual server and other feature will not be used. All of these will be still done by the 2Wire.