Having it be hollow will probably help. I'm not sure whether or not wool fiber absorbs other liquids (non-water based) in the same manner it absorbs water. You can probably run a quick test on a sample of similar thickness and firmness to determine that.
I still don't understand, given what you say you want to do with this piece, why you made it of fiber. It seems like you want to eliminate all the qualities of fiber so why not just make it from something like clay?? Maybe I just don't understand what you are trying to make.
I would be very interested in seeing photos of your project and to hear how it goes so do please keep us posted!!!