I saw that and planned on that being my second attempt. Right now I have an old iPhone cord cut up and I was just about to splice it to my helmet cord but then wondered about adding a small inline fuse to prevent melting wires if i was to get a short somewhere in the wiring. And I decided I didnt really want to be cutting up my only helmet cord without another one on the way incase it doesnt work.Not sure if it would work but you could try this and operate it backwards then intended maybe?? Just need a double end usb cable to go from battery source to this adapter to rca.
http://www.dg-electronics.com/?page_id=45