Tomato router: Bridge to Ethernet LAN, Devices access via Wireless

The solution was almost like Wireless Ethernet Bridge, except that Wireless Ethernet Bridge sets up the LinkSys Wifi as a "client" - ie. other devices can't connect to the Wifi on the LinkSys. (This is not obvious in the GUI, as the client/hosting wifi modes look identical).

Instead, I did this:

1. Set Administration > Password to something secure.
2. Wireless Mode = Access Point. This way clients can connect to the router using Wifi.
3. WAN = Disabled. Optionally set the WAN port to be used as an extra LAN port.
4. DHCP: Off. Uncheck this box. That way the router on the wired LAN can assign IPs instead.
5. Choose an IP Address for the Router. This was important to make sure you could still access the Router's admin page after applying the settings. IP should be within the range that the Wired LAN router assigns via DHCP. I also set the wired LAN router to reserve this IP for the Linksys (in \etc\hosts in my case).
6. Gateway = IP to your wired router's DHCP server. Tomato will send all request for an IP to the server you type in here.
7. Connect your wired LAN to the router & Reboot the LinkSys/Tomato router. Should be able to access the admin page at the new IP address you chose in step 5.
8. Optional: Enable Firewall > Respond to ICMP Pings. Helpful when testing the connection from other computers on the network. Can disable afterwards.
9. Setup the Wifi client access securely (in Basic > Network). Both WEP and WPA/AES worked for me, probably others will as well.

Clients connected via either Wifi or wired to the LinkSys now get IPs assigned by the wired LAN Router, and have full transparent access to the Wired LAN.

If you make a mistake (eg. can't access Admin page and cant fix it), the 30/30/30 reset will bring all settings back to Tomato defaults.