Activity for Marley

I posted a few months ago about my shape wear woes. Well now, three days before my wedding, I found the impossible. I bought the Spanx Suit Your Fancy mid-thigh body suit as a last resort. I had seen them in person and never in a million years...

My dress has a really low illusion back. I need some kind of shape wear that will smooth out the lower tummy without showing. Does anyone know of any brands or tricks that may work? Back of dressFront of dress