IK advice?
I am not sure equating bones with armatures will work very well. I did make up
and prosthetics (did you ever take Dick Smith's make up course?) and all that
on an amateur (occasional professional) basis for a while before I got my
current job, and I approached bones the same way and found it doesn't quite
work the way you think. The manual says use fewer, larger bones, but I have
found that more and smaller seems to work better, with carefully placed anchor
bones.
I am not an IK expert, but I don't think you can use IK as you desire. It
sounds like you want more of an elastic type of movement, and as far as I know,
IK doesn't have any type of setting to accomdate this type of movement.
You might be better off making many small boxes around the lips, and link them
to a center object behind them in the throat.
I got that idea from Glen Melenhorst and it worked a lot better than the way I
was trying before. You might want to try it.