I find , carefully drill a smaller diameter hole down through it - this will create a "tube" inside the thread AND warm things up,
you should then have more success with the mole grips,
Less heat damage to your bearings than with the "HOT - Spanner"
Charlie
Personally. I'd weld a peice of scrap to it, BWTH. Heat will help, but do try and keep it away from the wheel bearings (disk will act as a damn fine heat sink, though).