I did watch your replacement mouth tutorial a couple months ago. Your suggestion for the plastic wrap was great. I hadn't seen that before and I used your plastic wrap idea when making the replacement mouths for my lip sync test.
I took the process a bit further by making a mold of the mouth shape I cut out and then casting 8 more clay mouths and re-sculpting them to form the remaining mouth shapes I needed. That way there was the same amount of material used for each mouth shape and there were no size morphs during the animation. I also put the head in the freezer before sculpting each mouth shape so that I wouldn't deform the original clay head while I was sculpting all the mouths.
If you're interested, there's a really great stop-mo book that covers stop motion mouth replacements by Susannah Shaw ('Craft Skills for Model Animation') there's a link to it from my website in the amazon section (www.graydenlaing.net/store). Marc Spess's tutorial on sculpting and animating mouth replacements is also an excellent resource (http://www.animateclay.com/shop/index.php?main_page=product_info&cPath=1&products_id=103).
