Cliff,
If I ready your post correctly, you are asking if 12V power can be wired into the USB port to power the iFly. This is not possible, most USB port are only capable of 5V and have very low amperage. I am curious why you are trying to power the iFly from the USB. Since the iFly does not have an internal battery, you wouldn't be charging anything.
Maybe you have another 12V powered device and are looking to daisy chain the devices for power. Unfortunately, this will not work and could damage you iFly. The power input can accept both 12v or 24v, systems.