This is fantastic. I want to do something similar for my baby niece's nursery, except with little giraffes or safari animals. They wouldn't be 3D like your butterflies, though, just in different patterned papers.
If it were me, I would make a long, wide band of fabric in one of your colors and tie it around the waist, perhaps making a small bow and letting the tails run all the way down to the hem of the dress. And because I'm a serious fan of sparkly things, I'd embellish it with Swarovski flatbacks in coordinating colors. I am actually thinking of doing something like this for my own wedding dress.