Yeah, get a body shop to do it. Whomever did mine (my guess is 2 people) screwed one up. It looks like a master did it on the drivers side, its perfect. On the passenger side, there are at least 4 creases. Happened before I bought it, now Im trying to figure out the easiest way to fix it.
I've never done it on a Stang, but have used the following method on a number of other cars. Starting at the back of the fender, slide a baseball bat in petween the tire and fender. Then have a friend SLOWLY roll the car forward under power. As it does, the tire will roll the bat around the circumference of the fender opening. Don't try to get it all at once - make several passes using a larger diameter part of the bat each time. Done carefully and with several passes I've used this technique to roll fender lips without even cracking the paint.
I just bought the Eastwood fender roller. Looks like a great tool, well constructed. Have not had a chance to use it yet. I will post before and after pics when done.