DaGonz
Eats Squid
The forums would suggest if you're willing to craft your own cable, the you might be able to get it to go, or there's a couple of products out there that work with it. The forum would also suggest that it might be a firmware fix that may make this problem go away...Does anyone know whether the 800 can charge on the run? I browsed the linked review but couldn't get a clear answer on it.
check out forum.garmin.com
Of note, the 800 has the usb port in a much more "plug the charger in while on the go" friendly location.
HTH
Cheers
Spoonie