Hmmmm, thanks for that :)
It'd only be for my use, so I don't mind if it violates the spec as long as nothing melts or releases magic smoke.
The core32 page on ucapps.de recommends a power supply of at least 500ma, but doesn't go into detail about what peripheral boards that might be enough for, or whether it can get that over USB.
Perhaps Tk would be able to help us out here :)