Thanks. Never knew that trick.. assume you:

1) Get a tight-fit drill bit in the nipple.
2) Heat the drill to 'cherry'.
3) Try a Six-sider socket.
4) Rinse & repeat until thread cracks-off

Correct? Shove copper-grease in nipples.

Yes.

Shank of drill a tight fit in the nipple
Heat the drill (heat transfers into the nipple).
Cool it with water
Apply freeing fluid (ACF50 or similar).
Try to loosen.

If it doesn't, clean off combustible freeing fluid and repeat the process.