Hey guys! Look in the plastic wall stencil aisle at the craft store. A company called "Plaid" makes a stencil adhesive. Spray on the back of the stencil (don't soak paper) and allow it to dry for about 3 minutes or so. Then stick it to the pumpkin. It will leave very little sticky on the pumpkin. May be a better choice for faux pumpkins. The adhesive is designed for walls, so that it doesn't leave a residue on a matte finish.
I started using this at first for stenciling. I would find a design, print it out on paper, cut it out with a mat and exacto knife. It worked great for stencils I would only be using once and for placed a bunch of stencils together to create a mural.
As for the shaded areas of the stencil, I go along the border with an exacto knife about half way into the pumpkin. After I have removed the stencil and the cut out parts of the pattern, I cut a cross pattern all over the shaded parts. Then I use a variety of small wood chisels with metal tips to chip away to the desired thickness. Then I light the pumpkin up with a flashlight and check to make sure the thickness is even and is showing enough light through.