I actually fill the cavity with water and then lay my rolled clay sheet over top. I then spray the top of the clay so my roller will not stick to the clay.
Using a lot of pressure (I have to stand up for this), I roll all the way across the clay sheet and mould.
I then cut around my piece and do any other necessary adjusting.
I used some green colored clay and filled in the areas with mica powders to give it a shimmering effect.
My new Christmas package earrings are ready to bake.
* Note: I should mention that with my experimenting I prefer using water as a release agent with Kato and Premo clays the most. I found that when I used water with Fimo, the clay tended to "gum up" after and so cornstarch seemed to be a better choice.