I would imagine any USB powered iPod or iPhone plug would work.
A good sign is that none of the existing Apple battery products charged via the USB brick requires more than the 5VDC. So, if you have a universal USB car charger (ones that have one or more USB ports) you may not have to purchase a separate charger.
I am sure there will at least be a 3rd party solution for this
Woof, Woof - Dawg