That's what I did: installed a clean tomato (tomato-K26USB-1.28.9054MIPSR2-beta-Ext.trx) into the router and I used my old, trusty Atlantis Land WebShare 242W (it's a clone of the Billion bipac 7300, if memory serves me right) in bridged mode (so it acts as an ADSL Ethernet modem right now). I did not changed any relevant tomato option, just what I needed to get the ADSL connection up and running.
It works, but the transfer speed is artificially limited to 220 KB/s, as you can see from this image
www.morcilab.net/tomato.jpg (I'm a guest, I cannot post images link directly)
And this is with a couple of wired clients (one running at full Giga speed and the other at 100Mb/s). What's wrong with that? I tried to enable and then disable QoS to no avail.
Why is this 220 KB/s limit kicking in?