How to seal foam hair rollers to paint over them?

I'm doing up a craft project and these cheap foam hair curlers are perfect. But the only problem is, I'm not sure how to seal them so I can paint over them. I'm using a white glue/fabric glue/water mixture for the rest of the craft foam but these rollers are basically a sponge so I'm not sure this sealant mixture will be enough. Any ideas?