No magic wand tricks I know of...work slow and steady, use soapy water, silicone, or something to keep things sliding. I'd start from the inside in a upper corner with a glass stick and start to fold the gasket to the outside of the pinchweld. Work 6 or 12 inches from the corner in both directions a little at a time, easing the corner out first. Keep tapering away from the corner and try to get the whole top part of the gasket pushed to the outside, till you get to the other upper corner....if its not broke yet, you should be about home free.