Got the wire routed up to the head unit, and I'm really happy with the results. The long wire for the BOYO has an s-video connector at the end, so I had to route that through the vehicle. It got kind of tight in some places, but I ended up taping the ire to the end of a coat hanger wire to fish it through all of the tight spots.
Really pleased with the outcome - no visible wires, the license plate frame mounted camera looks great, and the picture on the head unit is crystal clear. I even drove around today with the camera on so I could keep an eye on everyone behind me
In case it might help anyone, I've attached a picture of the car and outlined the path I took to route the wire from the license plate to the stereo. If anyone has any questions I'm happy to answer them.
Thanks again to Lex for the tips.