OK, this is tested on Rev A1/A2.
Download Firmware 1.03 :
ftp://ftp.dlink.com/Gateway/dir655/Firmware/dir655_firmware_103.binAnd whatever firmware you want to run
Update the 655 to 1.03 and reboot. This will reset all settings to defaults. Don't bother saving them yet.
Go in and completely set up the 655 as you want it for acting in bridge mode.
When all settings are done and saved and rebooted (if necessary), set to Bridge mode and save settings and reboot. Now go in, set the Internet settings to point to your Modem/router and save the settings and reboot. Now save the setup to a file.
Now load your chosen firmware and reboot.
Go in and load your saved setup file. Reboot.
Done.
Mine worked with 1.35EU Firmware, but I tested it with a few in between and they all worked great. So you can get whatever speed or bug fixes are in your favourite Firmware, but use the 655 as a really good WiFi and network access point.
Not sure if this will help anybody now, but I googled this and got a load of pages that use one of the rj45 sockets to plug your modem into, rather than the WAN port. So here you go, for posterity if nothing else.