Matt, your overthinking this. [8D]

Take a vane and put it in the clamp. Without putting glue on the vane, find the spot where you can put as much offset as you can get and still have solid contact the whole way down the vane on the shaft. Solid contact is what matters, that's what is going to make the glue stay effective. Once you have found this spot, keep it there and set the jig there, and fletch all of your arrows there. I don't know if you can do it on a Bitz, but I mark it with a sharpie on my jo jan so I can get it to the same spot if I decide to do a different offset for another arrow/fletch.