Alas, I have realized that I cannot make a part of the body undergo a rotation along the axis of extrusion. So it can nod its head but not shake it.
This turns out to be the first major limitation in my approach to make characters with extrusion a mesh2 along a spline rather than with blobs in povray. I can think of ways to fix it, but it may ruin the portability to other users. It's already quite an unwieldy way of constructing characters.