How do I configure multi-gigabit internet?

If I were to put my XB7 gateway in bridge mode and then connect port 4 on the back of it it to my RAX200 router's multi-gigabit WAN port, how would I get a 2.5G connection back to my PC from the router? AFAIK, the LAN ports are only 1Gb. The router can be configured to use the 2.5G WAN port for internet, but AFAIK that would only work with link aggregation, and the XB7 doesn't support that. What other options do I have? I just want to have my gateway in bridge mode with the RAX200 router, and bypass the 1Gbps Ethernet limitation.