Most people don't bother to do it because they've gotta run RCA cables to the trunk anyway, so they just run speaker wires at the same time.

I came up with the idea once, not because I'm clever, but because I'm an utter moron. I'd just gotten done running all the power and RCA wires in a car once, put everything back together, and was installing the amp when I realized that I'd forgotten to run speaker wires. So I had a rather sudden need for a clever solution. Necessity is a mother. (Or something like that.)