.nomedia hides it from the player, but I still want to be able to play it. Just not with the rest of my music.
Continue to use the .nomedia file in your audio book directory and use a separate audio book player like MortPlayer for listening to non-music audio files like audio books.
Personally I use MortPlayer for audio books, BeyondPod for podcasts and the built in music player for music and things go pretty smoothly. I don't have audio books messing up my playlists and BeyondPod and MortPlayer have features better suited to listening to audio books and podcasts, respectively.