I think you need to define what you're using a little better.

Paper Clay: Using paper in pottery clay:  about 20-25% of the lump should be paper, and the rest should be clay.  The clay is fired as usual, and the paper burns up, creating a lighter-weight clay.

Products like Celluclay are mostly ingredients like plaster and starch mixed with paper fiber.  There is a bit of clay in the paper, but no real clay is in it.

Creative Paperclay(tm) is a product that also has no real clay in it.  I can't find out what it is exactly, put their website does say that.

You could make a mask form out of non-drying clay (like Plasticine brand), then form your papier mache over it.  When it's dry, you can remove the clay from the PM.

Anyway, can you give us more info?

Sue

Then you could make a mask from non-hardening clay (on a board) like Plasticine, which has oil in it.  Then apply your papier mache as strips or pulp or both.  After it's dried, the clay can be peeled from under the mask, as the PM won't stick to it.  Drying time would depend on how thick your papier mache is.  Putting it in front of a fan (at room temperature) would speed up the drying process.

Sue