I don't know how that could be done without just open sourcing the content for free and soliciting donations. Purchasing digital content doesn't work without kicking it down on the platform so it can't be pirated, right? That's the reasoning anyway.
The best way would be v4v so audiobook producers could still get paid.
I did a couple audiobooks for the school I lead in that format, set up with option to stream sats.
CTK Story Hour
RSS address: https://anchor.fm/s/1ba0100c/podcast/rss
There are others doing similar things with material that is no longer copyrighted.