I have coded a solution that runs on a little AVR board. It has been tested successfully with a JROK WSF. From my basic electronics understanding, I think it will work with original boards too.
It's a 5V device so I don't think it can damage anything, but I disclaim any responsibility for damage to your hardware.
How to use it.
You supply it with 5V and Ground, and then you will snip your control panel button wires ( Fire, Thrust, Reverse, Hyperspace, Bomb) and connect them to either side of the Reverse Fixer.
A jumper sets the Reverse Fix function default to On or Off. And reverse fixing can be turned on or off at anytime via a button combination.
The board can be unplugged and replaced by jumper wires to remove the device temprorarily from the circuit.
How to buy it.
Price is £27 inc post.
Contact me first to see what form factors are available.
Original Arcade Boards
If there is interest and someone can point me to a source for the original molex? input plugs and sockets, I could get a pcb with made that will plug in to the original harness.