Very nice analogy Steve.
Nevertheless, programmers and scientists are still trying to separate the two colours - even if they have to pick them pigment by pigment (a little easier if one would be magnetic…).
If the loop were really constant throughout or we had the original loop, your demand could be fulfilled - by spectral substraction.
The next best is to remove the center (with drum and bass mostly) and keep the right channel, where the melody dwells.
You can try it yourself by downloading this plug-in:
https://forum.audacityteam.org/t/karaoke-rotation-panning-more/30112/1
(Place it in the Audacity Plug-in folder and restart Audacity - it will be found in the effect menu “2D Stereo Toolkit”)
Simply choose “Remove Center”.
You can then split to mono (track drop-down menu) and remove the left (upper) track.
More isn’t possible - as far as I know.