I have the 3500L and two $30 Trendnet TEW-637AP's which are designed specifically to do what you want. I did what you said but in reverse.

WDS only supports WEP so that wasn't an option for me. The Trendnets were configured into AP Client mode. What that means is that the Trendnets connected as AP clients (not WDS) and were using WPA not WEP.

Then I put duplicate SSIDs, AP Names, and hardcoded channels on the Trendnets. This let me move from room to room, floor to floor using one WIFI connection and roaming between WIFI APs. This worked well for my AXIS WIFI cameras which are a pain to configure. No matter where I moved the Axis camera, it connected using the same settings. I had to use WPA to support the Axis cameras, thus no WPA2 for my case.

I am running Tomato now on the 3500L. The instructions for doing this on Tomato are located here;

http://www.wi-fiplanet.com/tutorials/article.php/3810281/How-to-Set-Tomato-Fi...

Now this should be easy:-)

Remove the covers from the router, prepare some screwdriver etc. that allows you to short pin these connectors:

http://chainsawdwarfrider.free.fr/router-shorcut.jpg

Connect a PC to the router and configure it's network card to 192.168.1.1.

Now important part:

press the reset button and power on, still hold the reset button for 30s release the button and immediately short the pins, now you should be able to constantly ping the router. If that the case you can tftp an original netgear image to it.

The serial method requires to solder some pinouts, this looks easy on the pictures but is not that easy without the appropriate equipment. I did this at work where I had magnifiers, a bench vise solder sucker etc.