How to remove seized square taper cranks

I was really rather worried about this.

This is a crank arm and the BB from Pratiwi's bike. Although I managed to get the drive side crank off, the threads in this (non-drive) got completely stripped when trying to remove it - with a crank arm remover of course - but the arm itself is made of very soft metal and they easily strip

Now... those threads look OK, don't they? That's because I gave up and took it round to the LBS (KOM in Cammeray) where the talented Mr Burgess cut some new threads and also ground a nice slot in the top of the arm which loosened it's grip and the sucker then came off.

FWIW, he then had no issue getting the BB out, but I tell you, I couldn't shift the side I got the arm off at all. Cheers Waz!