Sorry it took so long to follow up, one craft comes and goes and I quickly am on to the next! But here are the results of my DIY Super Kinder Eggs. The plaster did crumble quite terribly, and so I won't be using that again, but the kids loved ripping them open!
I finished them with two layers of just colored paper strips dipped in glue+water. Then I took a sharp knife and cute openings to stuff the toys, and did one big piece of colored paper to seal it up.