I'd be really interested in seeing how you get along with fitting a FET to a QD - please if you get time take some pics and post up :-)
If you could find one small enough, like a PICO maybe an opp to fit it inside the trigger housing, longshot I think. I was really impressed with the QD box, although I haven't worked on one just opened it up, the anti-reversal latch was firmly held in position and as I said before the safety arm has been removed so no more messing around with that annoying spring.