Face Expressions from one mesh to another I have 2 human faces in a scene, one of them imported with a heap of keyshape facial expressions, 
and another mesh which only has one keyshape. open mouth.

I would like to know if there is any way to use mesh deformers or other modifiers to somehow copy the general changes of a different mesh to mimic it.

Maybe there is an advanced way with bones / drivers or something else.??

some of the facial expressions are really cool, at the worst case I would copy the ones I like one at a time manually editing mesh for keyshapes, but if there is another way I'd like to learn.

The following 3 images show the Face on the left has some expressions I would like the face on the right to copy..
If the meshes are different regarding their vertice (count and inter-vertice-connection - the "edges") there is no native way to do this - at least not with native blender tools. I don't know of any addon, which does this - I often need to have such a tool and didn't find any.

The reason is, that the shape keys are recordings of vertex displacements. 
Think of a sphere with shape keys and try to transfer them to a cube....
(ok...that example is extreme...;) )