Yes, I was thinking about how to connect the two while riding, and that sounds like just the way to do it.
Thanks all, appreciate the replies.
For those who didn't read it, I mentioned in my France cycle tour thread that the Garmin Edge 1000 provided with the tour hire bike only lasted 9 hours on a 9 hour ride (elapsed time), and then it turned itself off just before the route guidance could tell me where my hotel in Corps was. It turned off just as I passed the "Corps" town boundary sign, so rotten timing. So if 9 hours in route guidance mode is typical, then obviously it needs help to last for a long day's ride.