For macs you can get a power adapter that plugs into your usb drive - maybe you could find something similar?
Cite? I've never heard of such a thing and knowing what I know about USB ports (which really isn't all that much, but it's a lot more than nothing) I find this unlikely. Google isn't being much help.
My mistake - just checked back on the shop - it is called an 'Apple USB Power Adapter' but it is for iphones and ipods. I had assumed from the name and the fact I was asking the store for chargers for my macbook that it was for laptops.