Originally Posted by repechage

Gravity is a power force, I have seen this before and yes some shells are that malleable.
As they are, we have had to effect this repair a few times, always most trying on a new frame...
Depending on what shop I was working at there are any number of ways.
The trick is keeping the paint intact.
If you have a solid workbench, drill a hole with a hole saw the OD of the shell, cut it back to allow the BB shell to nest, then using a brass or copper rod with a rounded end and a helper holding the frame, work your way around and into the flat region. When your eyeballs tell you it is near, chase the threads. You do not want to go beyond where you need, just shy with the hammer work, let the tap return things round.

The Exhaust tube expander might do the trick too. But I would be sure to grease things up and still finish with a tap.