Whats the best way to remove a seized internal BB?

I've tried leverage, I've tried rubber mallets, I've covered it in oil and left it overnight. I'm worried that if I apply anymore force it will thread the splines and write off my frame.

Thanks

Hold the tool in a vice and use the frame to turn it in the correct direction and gently work it forward and back.Done a few like this.I usually leave them soak in wd40 for a day before.

Just a thought. You are turning it in the right direction?

(the rhs is a lh thread)

I found using a bigger meatier wrench did the job. Adding just a few centimetres made it much easier. Applying pressure steadily for a few seconds at a time seems to work better than sharp yanks too.