Thanks for all the suggestions. I wish I had asked before I started, as it would have made things easier. In retrospect, I should have made the whole thing off the bra, made a lining as well, and then joined the two pieces with the real bra in the middle. But I started adding pieces as I thought of them, which made it more difficult. And I wish I had thought of the folded dahlia - great idea!
I'm making progress - I made a bias tube of fabric which I folded over the edges and am hand tacking with a tapestry needle and pearl cotton - it's the only way I can get through all the layers. Should be done in a couple days and I'll try to remember to post photos.
Thanks!