Having reviewed most of the replies now, I have another suggestion that may work and I don't think it has been mentioned.
This depends a bit on the exact location of the ball, but one could drill the touch hole for a liner, install grease fitting (before or after threading, depends on what sizes you have available) to push grease, clean up/thread and finish liner installation.
Both bore lights and bore scopes are dirt cheap these days.
Don't "try" a gunsmith who doesn't understand how gentle he must be with our "soft" steels.
The bloke speaking of acid was standing on the wrong side of the ball. Base, not acid, is where one might find a non-corrosive substance to eat the patch. Specifically, I used to use a lye vat for soaking clean cast-iron skillets. Could leave iron in there indefinitely with no concern. Organic material would be lifted eventually.
Hmmm, we should try this AND I have all the proper ingredients: 12L14, lye, denim for testing. Will report if I actually do such.
Whatever you do, learn how to do it well because there will be another event quite similar. It's simply part of playing our game with the toys we choose.
Despite what you may have heard there are ONLY two kinds of BP shooters:
those who HAVE dry-balled and
those who are GOING to dry ball.
Congratulations on moving from the second category to the first.