A clothes iron will work (but I wouldn't do it again.) Easiest approach would be with an additional convex form for the waist. Best results by clamping in place once bent over the form, allowing to set and then spritzing and slowly ironing again while in place, then again, leave plenty of time to set. It is far from ideal, and her indoors won't thank you - worth making or buying a bending iron, fox system or heating blankets.