My friend had to do this for the play she was in.
You saran wrap your breasts as best as you can, then ace bandage them.
But there is a huge risk for pain. And if you are tender there, it hurts like a @!#$@%!.
But it works the best.
Then there is duct tape, but that is just insane.
The easiest way for me, is to wear a really tight shirt that flatens me and then wear ace bandage around my breasts. It's more secure and it cuts me down about three cup sizes.
I hope this helped you.
<33