Success!!! I think...
First I tried the tow method as akb suggested, but I didn't have any thin cable that was strong enough, so it kept breaking.
Next I tried to drill 4 holes in the front and put fishing line through those so it grabbed the bolt and wrapped around the bolt several times. That came untied and wouldn't work too well.
Then I ended up with what I have now. I ran a screw through the front and grinded the ends off, then put a nut with a V grinded in it on the end of the rod to ensure it didn't slip off to the side. It was still having problems because I had too many teeth on the new part. It looked really cool and had teeth all the way around, but I had to grind all but 6 of them off. It works now and punches a perfect hole. Fortunately it has enough friction to not shoot out when I fire the gun.
Unfortunately, my pressure gauge seems to have broken
so I didn't get to see if it would work at lower pressures because I had no idea what pressure I was at.