i would take it out of the frame and put it between 2 sheets of glassine. then i'd use a spray bottle to very slightly moisten one side each of 2 pieces of foamcore. then i'd sandwich the 2 sheets of glassine and the print between the slightly moist sides of the 2 pieces of foamcore and apply some weight. letting the print hang out for a while in that slightly moist environment should lessen the visibility of that roll bend. i have tried this before with prints that i didn't care about and the results were quite good. the roll bends didn't disappear completely but they were definitely softened quite a bit.
alternatively, you could try reverse rolling it around a tube with an emphasis on that area.