Deform via 'Cage Edit' but preserve edges/borders?

Hey, this would be a tremendous improvement of my workflow for upholstery furniture designs to make them look a bit puffy.
I don’t like TSplines so much. So is there a way to lock the edges when using the 'Cage Edit" command to preserve the edges to the adjacent surfaces and not destroy the edges? thx

actually it would be even more awesome in Rhino V6 to lock the edge positions and randomly position some points to use them as driver for the transformation. Like in Photoshop’s ‘Puppet Warp’.

Hard to see how to do that cleanly with surfaces - It would be much easier with meshes/SubD.