I don't like the application, especially since we have such cost effective business series WAP's out there like the WAP200.

And, I'd like to simulate the application normally before i give an answer, but my WRV210 is out at the moment.

My steps would be with the WRV210;

step 1.  adjust the LAN setup options of the WRV210. Set the IP address of that of a free IP address on the existing routers LAN interface

     This should allow you to be able to manage the WRV210 from the existing Local Area Network.

step 2.  disable DHCP on the WRV210

step  3.  plug LAN port, say port  4 into the existing WAN  routers LAN switch .

(remember to save options as you go)

I would just ignore the WAN interface and it's settings as then i would need to alter the operating mode of the WRV210 from gateway to router mode.

This would mean I would then have to play with firewall setup on my WRV210 and the routing on my existing router.  So leave the WAN interface unconnected.

hope this helps

regards Dave