use that for their own sample libraries. I don't mean hire pro session musicians to play on their songs, just get some cats that play (they don't even have to be great players, as long as their tone and sound is good) and then record them and use that audio to chop up their own samples that they would own all the rights to.

When I was doing beats I would always sample and chop up myself playing bass or keys, and I would use recordings from jam sessions/rehearsals with other musicians as well as a source to chop my own samples. If you want clean samples then record an individual musician playing around on his instrument for around 10-15 minutes, and find small chops that you can flip and use out of that. If you want dirty/grimy samples, record a group of musicians jamming for 10-15 minutes and you can filter/chop it up however you want. If you do it that way you can make it sound like it came from some old rare album that noone is up on. If you want to get creative, record some musicians playing instruments outside of the normal "band" setting - like someone playing a harp, or cello, or sax, or whatever. Chop and flip it up, and you've got something unique.

Since you aren't having them play actual parts, the musicianship/professionalism of the musicians doesn't matter - just the sounds that you are recording. And you would have a library of samples that could be used on multiple tracks. It wouldn't be expensive at all - I don't know why there aren't more producers doing this.