An idea is to use a large nut and bolt.
Pass the bolt through the shell and poke it out of the seized cup. Screw on the nut with a washer.
As you tighten the nut, it will grip the cup and unscrew it. The drive side has a LH thread, so by tightening the nut clockwise, it will turn the cup clockwise too.
If you have Italian threading, ie the drive side is RH thread, do the same, but the other way round - if you see what I mean.
Pass the bolt from the outside of the drive-side cup, screw on the washer and nut inside the BB shell. With a long socket and extension, you can tighten the nut. This will grip and turn the cup the correct way for unscrewing. ie anti-clockwise as viewed from outside.
If that doesn't work, resort to the hacksaw method!