I worked on my next piece for the Exquisite Corpse Challenge today and ran into something that I thought might help some of the others in the group, so thought I'd post a little tutorial on how I do it. Anyone who is familiar with varying forms of applique will already know how to do this. This is a good way to cover up irregularly shaped forms.
you will need: freezer paper; a scrap of opaque material slightly bigger than the area you wish to cover; some spray-on starch; a little plastic container; your iron (no steam); and either a q-tip or your finger.
Step 1 & 2: trace the exact shape you need to cover onto the paper side of the freezer paper (you will have to reverse the image in order for it to end up the right way when you are done). Cut out the shape slightly outside the drawn lines.
Step 3 & 4: Press the 'waxed' side of the freezer paper onto your scrap of fabric. Cut around the paper, leaving a good 1/4" outside. Clip any corners, and you will also have to clip a bit around any rounded pieces in order to help them ease in to fit.
Step 5 & 6: Spray some starch into your little container. Use the q-tip (or your trusty finger!) to moisten the seam allowances. Fold them over and press.
Step 7: At this point you can remove the freezer paper (I didn't, because I wanted it to help mask what was beneath). Place, freezer paper side down, over the area you wish to cover and simply hand-stitch around it to hold it in place.
Voila! Hope this might help someone. And, Corpses-peoples, this is NOT the shape I used so I'm not giving anything away.