|You could daisychain the old router to the new one and setup your wireless network on the old router.|
For more info on how to accomplish this, click on my name above and read my "how-to" guide about adding a second router to your network.
You'll want to use the version wherein you interconnect the two devices "LAN port to LAN port" and have the second router in the same subnet as the first.
If you have a wireless network setup on the new router, I would disable it once you have the second one connected, configured, and working.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.