Converting Front AUX to Rear AUX

I know this is possible. Has anybody done this, able to provide a guide to show me how to do this with my HU. I have a JVC G140 with absolutely no customization. I had a Pioneer DEH-5900IB before (w/ rear aux, loved it), but was stolen along w/ my subs/EQ/amps. I would greatly appreciate anyone who is able to help me doing this.