I haven't had to remove a nipple but I will say that Kroil + time has worked for me in a number of situations.
I wanted to pull the barrel from an Enfield P-17 which are famous for being all but impossible to remove without a relief cut and 6 foot cheater bars and even then I'd probably bend the action. I stood the action muzzle up in a corner of my bench and whenever I noticed it there I'd put a few drops of Kroil on the barrel/receiver joint.
This went on for three months before I decided to attempt to pull it. I set it up in the barrel vise, attached the action wrench. I dropped a hand wrench and as I bent down to pick it up I leaned on the action wrench and the action spun right off.
If you have the time, a little Kroil every few days, then a drill and easy out may do it.
