How do I make certain vertices resist movement

I’m creating a shape key (closing a jaw on a dragon head to be exact) and I’ve been trying to work out a way to keep certain vertices within a proportional fall-off field from moving while others in the same field are being moved uninhibited. I know the basics of weight painting but can it be used to do what I want? Or is there some other method to make them stick to their spot while others in the field of influence move? I would like the transition between the vertices with full resistance to the proportional fall-off field of influence and the ones with no resistance to be smooth though (such as the effect that shading in weight painting would have).

Shape keys work by moving the vertices along a straight line between two points: where the vertex is in the basis and its location in the shape. The slider tells blender how far (.500 is half way) to place the vertex along the line. When something, like a dragon jaw, moves, it actually moves along an arc from the jaw hinge. As long as the angle isn’t too large, the straight line motion produced by a shape key is close enough. But when you are moving along a relatively large arc, the straight line isn’t a good approximation anymore. One work around is to use two (or more) shape keys, another is to use driven shapes.