More than once I've seen a local smith get a straight piece of spring with a diameter big enough to fill the channel. Pulls the rear pin halfway out, slide in the spring in the groove. Wiggle it around to get it under the detent. Rotate the takedown pin so the groove is away from detent. Slide in a piece of round stock that's snug in the pin hole. Slowly push out the pin with the round stock. Take the new pin and push out the piece of stock. Make sure the detent is engaged by trying to rotate the pin.
A little while back I watched him do at least 4 in a row in minutes. At the time it was for the Noveske marked pins, that some guys needed to make their rifles faster.

