I agree that steaming should work - it's used for clothing in retail stores and draperies when hung by decorators all the time. You'll want to have the quilt hanging, then gently steam by holding the steamer near, but not in contact. Gravity will help relax the crease.
Your home iron might not steam in the vertical orientation, but you can try it. I use a Velocity portable steam generator as both iron and steamer (saving up for a Laurastar).