You could take the book (or the movie
) and make a plan what you are going to do. I like to plan, what "tools" i'm going to use, like: An atonal melody with the bow, or transitioning from clusterlike double stops to high harmonic playing, or playing entirely percussive on the bass with hands and malletts, the list goes on. So you could plan what you are going to use in each situation, without completly preplaning each note.
You should keep in mind, that you are playing the accompaniment to the story teller, so your musical concept should be much more static, than a typical solo bass performance. If you play like Dave Holland on Emerald Tears, nobody will listen to the story anymore.
And: Are playing while the story teller is reading, or are you silent most of the time and commenting, when the text stops, like an ancient greek choir? Many possibilities, lots of fun if you have a plan, no fun if can't play because you can't decide one of the many things to do, in the moment.
P.S.: Hope it's understandable. English is not my native language.
Interesting Project! 
