Why do you want to use audiobooks? The usual reason is so that you can learn or enjoy a good story while you are doing other stuff. If that's the case for you, then do that stuff and your lack of physical motion is solved. If you have another reason, have you considered taking up walking just to enjoy your audiobooks and for exercise? How about knitting? Woodcarving? Keeping ones body occupied is not an unexplored problem.

As for speeding up, I was a lot more sceptic that it would help me concentrate on videos before I tried it.