Interesting,

I have only the following three JR / Spektrum radios

DX6i
6102
Quatro

Each of these does indeed require a battery in it to work as slave. However; each DOES power up for me by simply plugging in the trainer cord, (I very nearly ran my battery dead by leaving the trainer plugged in when I was using my Quatro TX for the FMS simulator).

I apologize for assuming all would do the same, since I've no actual experience with them. I simply assumed all JR / Spektrum would work in a similar fashion.

I am one of very few who uses JR / Spektrum at my club, (More are buying Spektrum but I'm the only one with practical experience). That said, I would be very interested in a synopsis of the final details you and your club determine if you would be so kind as to pass it along sir. (Since we all know the manual is clear as concrete in some areas [:@])