Laminating paper with PVA will work for simple curves, but I'm not sure how well you'll be able to form soft wrinkles and complex curves. Perhaps a single piece soaked through would suffice. Never tried it, myself.
Looking at other options,
careful application of heat will make plasticard quite malleable. I've seen some very convincing banners made this way. Laminated foil (standard aluminum stuff nicked from the kitchen) is a also a possibility, but you have to be careful, otherwise you'll end up with dozens of small, sharp creases instead of a few large folds.
If all else fails, bend some plain old printer paper as best you can and say it isn't windy, today.