...doing some more thinking on this...
Now wondering: I have the Carnetix 2140. Should I just hook up an M4ATX (or similar) to its output? Configure the M4 to leave the USB bus always powered... I could still use the 'dead man timer' option on the 2140 where it would completely cut power after the desired time frame...Where would this break down? What am I missing? ....hmmm, how would I actually wire the ACC and constant battery of the M4?
Just brainstorming / thinking aloud...thoughts / ideas?