I bet there's probably a couple people out there with 770s that have a gem of a cable that they didn't realize they have.

Many 2.5" external USB enclosures come with a "power injector" cable that has a normal USB A connector, a power-only USB A connector, and a mini-A cable.

With this cable, ANY USB hub without an integrated upstream cable can get power injected upstream to the 770/N800.

If you get a gender changer, then you can use it with hubs that have an integrated upstream cable.

So you could, for example, use this battery-powered hub, and inject power from a downstream port upstream.