I did the last one with Caustic Soda. not pleasant but effective. Took a week of changing every day, the heat generated was high and the stuff is unpleasant, rubber gloves, splash proof clothing and a mask required. Poured it in thru the BB shell, made a slight mess on the paint but I resprayed it anyway so no problem.
Have tried the twisting in a vice method but the fear of cracking the frame stopped me getting brutal with it.
Caustic Soda only to be used on steel frames obvs....