OK, all we need to do take the 1.2 firmware's version string and put it into the 1.0 updater's data fork replacing one of the strings of the firmwares it knows it can update. Then you can run the 1.0 updater and hopefully that will trick it into thinking it can install the 1.0 firmware.

I will work on it later tonight and get a patched updater file to you...