Soarer's WYSE Converter firmware should work with it.
You would have to get a Teensy 2.0 (or similar board with the right type of microcontroller on it), solder a 4P4C connector or cable to it and load the firmware onto it. If you don't install the converter inside the keyboard's case, then you might want to build a box for the controller also.
BTW. There are also people on the forum who lend their services if you don't want to/can't solder yourself.