Plasti-dip! It comes in a spray can and is essentially spray-on rubber. It is a sealer and a primer, so its ready to paint as soon as its done. However, it does eat styrofoam, so I would test it on a little but of the floral foam first. I know for a fact that it doesn't eat craft foam. Its also very smelly, so make sure you have an open area to spray it.
You can see how well it coated my craft foam here: http://www.cosplay.com/showthread.php?t=307906