I have not done this as the 18mph issue is not a problem for me. However, You could rewire the disconnect to operate with a switch and put a resistor of the correct size to simulate the load the disconnect presents to the jeeps controller.
I think jeep uses a current sinking output and it measures the current that flows to the disconnect to determine if it is on or off and if its working properly or not. With the schematic for the jeep and specifications for the disconnect it would be easy to figure out.
You would not have to energize the disconnect with that same tehnique. Just get 12V to it, I don't know if its polarity sensitive or not, easy to determine.
I'm suprised this mod as well as locker overides have not been packaged and made avaiable from one of the aftermarket parts suppliers. Might be a liability thing.
2008 Rubicon, 4 door Detonator yellow, 3.5" lift, Motech LS 6L engine conversion, RR Skids.