Is it possible to parent single bones in an armature to a mesh in order to drive the bone motion based on the mesh motion?
no, but you can make an empty the child of a face and use copy rotation/location constraints on the bone to follow the empty
[it looks like trying to do a vertex parent of a single bone crashes blender]
I played around with using the copy rotation/location constraints directly between the bone and the mesh, and that would have worked well I think except it flips the bone 90 degrees from the angle it should be at for some odd reason and nothing I try seems to alleviate that problem. Clearing the Rot angles of the bone or the mesh have no effect so I am pretty stumped at this point.
You could add the mesh object as an driver to the bones ipo curves. Here is a simple example. Look at the properties of the bones pose ipo curves to see where u add the object driver.
After looking back over you question, I realize that I may be mistaken. My example is for a whole object, and not for a mesh within an object.
I then added a second mesh, Ctrl-H to make a hook for it, and used the empty as a driver for the second bone. Im still not sure if this is exactly what you need.
http://www.cafes.net/ladyb/example2.blend
I worked out a solution using empties parented to the mesh objects and then IK constraining the bones to those…That seems to be working pretty well so far. The IPO driver idea is intriuging to though, I’ll have to look into that, thanks for the sample link.