Hey Bill,
while not exactly what you are talking about, Motionographer has a few examples of replaced heads, which use a very similar tracking technique to replace the features. It was a "Quickies" on their site... so I could not find a direct link, but there are the examples they posted.
http://www.glossyinc.com/sleeper/getty.html
http://www.sidefx.com/index.php?option=com_content&task=view&id=1045&Itemid...
http://static.swiss.se/public/portfolio/Sony__.mov
I've only done that kind of stuff to fix blemishes on anchors faces... but I think your first approach might be the best. Having as much natural skin texture to work with will help blend the seems. Take some pictures too, with a still camera that will come in handy if you need to patch skin.
The mask approach may not be the best choice, unless you're up for replacing the whole head, and trying to color match that as skin doesn't seem like the easiest thing to do. I ran across a post on something similar to this a few weeks ago (can't find it now, doh!) and there was a lot of discussion about the need for markers or not, since they would need to be removed in post. The face, eyes and nose, should have enough detail to use as tracking references. Saving you a lot of clean up in the end.
I think you're on the right track. Do some tests if you have the time. Not sure what you are planning on using for tracking but both Boujou and Syntheyes should make that an easier process. If the subject does not rotate much you might be able to work some lock down magic with Mocha.
-N
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