Using a switchback for the rear signal + backup light is pretty smart.
I think some (all?) switchbacks will only turn on the main if both are powered at the same time, but I doubt you'd need backup light and signal light together all that often. And since you can consider them to be basically two independent bulbs sharing the same ground, this mod is also pretty simple.
I love the YouTube comment about adding a physical switch to force the backup light to turn on. Tailgaters beware. Blinding light ahead.
