I have this one instead of lighter in Marilu dash ..
http://www.amazon.com/gp/product/B00IRJH8CE?psc=1&redirect=true&ref_=od_aui_detailpages03
I have one of those in my rear compartment.
What I am looking for is a dual port USB plug that fits in a factory slot where one port is solely used for charging and the other port is an extension of the input into a head unit that creates a nice finished look instead of having wires routing all over the place. If you look at the picture I attached above you can kind of see what I'm talking about. Two wires (+ and -) and a USB extension hookup.