You can try to get it out as Sage described, but I have never had any success doing that. Nothing holds well enough in the seal material to pull it out, as the fit between the case and the shaft is very tight. I tried exactly the same thing, but the screw just kept pulling through the seal material, and I ended up destroying the seal badly enough that there was no way to pull it out with anything from the outside. Before you try it, make sure you clean the outside of the shaft very well, as a lip of grime will build up on the shaft against the seal, preventing it from moving.
Try what XP said also, I have done this many times with fork seals, and it works. I use film negative on the fork seals.