I'm tempted to try this on my DX7 actually, had a lot of problems with battery life during events. I actually modified it a bit a while ago to take a 'standard' charge plug rather than a Spektrum one (as me being me, I somehow managed to order a set without a charger) and the main outcome of that was being unable to do much testing ahead of Barnsley as the heat from soldering blew the transmitter fuse :P

From memory the voltage regulator's in more or less the same place so I'll let people know how it goes if I do give it a go.