As we know, Tomato does not support running as a Repeater or Repeater Bridge like DDWRT (for now) and the only way to make it work like a repeater is to use it as an AP + WDS. The downside with WDS is that it forces you to downgrade from WPA2 to WPA, it does not take full advantage of Wireless N, and it wont work if your main router does not support WDS.
My workaround does not require that the main router supports WDS. It only requires that the main router can broadcast two SSID at the same time. This workaround (and granted its not the best but it works fine) is to create one SSID in my main routers that only the repeater routers will connect to, and then have all routers broadcast another SSID that all clients will use.
The steps to make this work are the following:
Step 1: On the Main router, set a unique and different SSID from the one you plan to use and set a good encryption level (i.e. WPA2). Dont broadcast this SSID.
Step 2: Connect all client routers to the Main router as Wireless Ethernet Bridge using the SSID and key from Step 1.
Step 3: On all routers (Main and Repeaters) create a new Virtual Wireless as AP and use the same VSSID name and encryption key on all routers (use a different key and SSID name from the one on STEP 1 or your repeater routers will selfconnect and become pretty much useless).
Step 4: Use the VSSID and key from Step 3 for all your clients and only use the SSID and key from Step 1 to connect more repeater routers.
Step 5: Disable DHCP on the repeater routers and set the gateway and dns to point to the main router.
Step 6 (not sure if it makes a difference): Change the repeater routers to work in Router mode rather than Gateway mode.
Step 7 (optional): If you use Static DHCP/ARP and you hook a device that requires static IP to a repeater router, you need to remove the Static DHCP configuration from the main router and put it instead on the repeater router it is connected to.
I know this configuration is more complex than with ddwrt but with this you can reach full wireless n speeds of up to 300 mbps ( 2 channels ).