Hello, I've been playing with a small circuit for my Bunny...
I've put three USB connectors on a small board, 1 for the Bunny, 1 for the Target PC, and a switched one for a small battery bank (I use a cylinder type).
I have just run power from the battery bank connector to the Bunny and did not hook up power from the Target at all.
With this setup, I can run attacks on USB 2 only devices; and, more importantly pre-boot the Bunny before the attack... Flip switch, wait for Bunny to boot, then plug into Target...
I don't use the Bunny for keyboard injection, btw - I still prefer my Rubber Ducky for that.
This kind of setup could easily be added to the base Bunny, or as an alternative hardware version - with a single usb jack on the back to accept the battery bank connector.
A more sophisticated circuit could be setup to detect if power was available at the Target and allow the battery bank to be removed. Pre-boot Bunny, plug into Target, pull and palm battery.
The only complication is that it would be a lot of torque on the Bunny's main connector if the battery had to be left connected for a USB 2 Target...