Just like you needed a heat gun to soften the paint when you did roll them, you are going to need the heatgun again to soften so it doesnt crack again.
Though I would imagine the paints plastic region(as in a material's elastic and plastic regions regarding deformation) will have already been stretched so the paint may have slack and MIGHT get a little wavy.
Good luck, I would work very slowly working the entire lip a little, then going back and advancing it etc.
Hope that helps some
