yup. Seems to have been around for a long while. See thoughtfix's blog as he has all the information.

You need a usb power injector, mine is 2 flying usb sockets, with all 4 leads connected and a flying usb plug with the +5v and gnd lines connected to the sockets. Works with the plug connected to a PC, or a powered hub, or one of those car chargers with a usb socket fitted. You also need to have the 770/800 in usb host mode, then it works. Just mount the disk and away you go.

I need to get canola to scan the media on the disk now and I'm done.