Alternative to sheetmetal shrinker?

The way to shrink a section is really to put an intentional "wrinkle" in the spot, then slowly work the wrinlkle flat again without letting the part straighten out.

1. Put the wrinkle(s) in place
2. Clamp both sides tightly
3. Work the wrinkle(s) flat.

Mechanical shrinkers, though they work, they to it differently and it's not the best way. They scar the hell out of the metal.

More small wrinkles will be better than one big one