How to get a rounder butt???

So, I've been pretty much confident with my body except for one thing...I have a really small butt. My friends have made jokes about it, all love, but it's still one of my biggest insecurities. I'm planning on getting surgery where they transfer fat from other places into my butt, though I wanted to see if I could do some exercises now until then. Less of a square shape and more of a heart.