is there any way of getting to listen to just the backing vocals of a song?
No, I think that the instrumentals/karaoke are the best option actually.
Maybe with some songs that are remixed in 5.1 surround you can get small parts of some backing vocals, but that'll mostly be with other instruments, but maybe there are other options?? I don't know.
"If there's a God or any kind of justice under the sky
If there's a point, if there's a reason to live or die".