Assign "Shape Key" from rigged mesh

I’m trying to achieve the following deformation:

I have a mesh “A” with a Shape Key from a mesh “B”, the mesh “B” is already rigged. I want to use the deformations of mesh “B”; but using “Join as Shapes” I get just the current state of the mesh “B”.

Is there a workaround or addon to have the mesh A always updated with the current deformation of the mesh B?

Thanks a lot!

Ok, there are no solutions… yet.
I really hope that this tool could be implemented soon, is a morph modifier. But for now only works in the following bundle:
http://www.graphicall.org/blender/wi…keywords=56383