This may seem an odd question but:?

Our college does a huge Halloween Concert every year, and orchestra partner and I have decide to go as Batman and the Joker, me being Batman. The costume I have consisted of a batman chest piece that is designed to fit a man. I have pretty large breasts (D cup) and I'm looking for a way to hid them so the piece fits a little better.

I've seen things like binding them, but would that work for someone my size. Or is there another option that would be better.

Thanks everyone for your answers!