I had the same problem with one of those plastic cup shimano b.b. in a alu frame I found it worse to get out than a seized metal one as I could not resort to my usual methods. Luckily I was at my parents house and my dad has a Phd in removing stuck items. It took the best part of an hour but the best way was a series of very small holes close to the threads and eventually it came out. We did damage the threads a bit but II got my local guy at Perry's cycles to chace the threads out when he fitted a new b.b and all was fine.
I had the same problem with one of those plastic cup shimano b.b. in a alu frame I found it worse to get out than a seized metal one as I could not resort to my usual methods. Luckily I was at my parents house and my dad has a Phd in removing stuck items. It took the best part of an hour but the best way was a series of very small holes close to the threads and eventually it came out. We did damage the threads a bit but II got my local guy at Perry's cycles to chace the threads out when he fitted a new b.b and all was fine.
I empathise with your problem.