You would finish the sides BEFORE cutting the gap all the way down, that way you can just chuck it like normal, finish, then cut the gap down to axle sized last. Otherwise, the axle section becomes a big weak point and you'll likely snap it trying to finish the other side.
If the axle is already done, you're.. um.. kinda screwed really. Unless you happen to have very deep jaws, I can't think of any way to do it offhand.
Kyle