I know this is a very old topic, but I stumbled across it while researching QDII activation/indicators.
I've done a 'prototype' by just tapping into the DC feed to each solenoid.
Details on my blog if anyone is interested;
Jeep WH/WK QDII eLSD activation indicator LEDs prototype | James Laugesen
This rough setup has been good enough for my needs for a while; it's handy to see what the eLSDs are doing in certain situations.
I've been working on a more elaborate project to control the solenoids (aka, control the "locking".), and also determine the differential oil temperature (very inaccurately at this stage.) via the solenoids.
Still the same general concept; just tapping a microcontroller into the DC feed, rather than interacting with the CANbus (which has proved very difficult for the FDCM, it handles most of the QDII logic entirely internally, controlling the components directly.).
The FDCM seems to be quite tolerant of external 'signals' on the solenoid DC circuits, not throwing codes and shutting things down like some other circuits.