I thought you just jammed a jack handle or aluminum baseball bat in between the tire and the fender, then rolled the car back & forth.

To be fancy, and if you happen to think of it before the new fender is hung on the car, place a beach towel on the concrete floor, put the fender outside-down on the towel and start carefully hammering w/ a rubber mallet. If you're careful, this can actually be done w/o damaging the primer and get's another item in the Hitch-Hiker's Guide for how to use your towel.