Using vertex shader to extend portion of hand.

Using oF 0.8 for codeblocks on windows7, specifically ofxkinect,
I am trying to achieve an effect in a game, where, the palm of the hand stays intact but the rest of the arm extends and the user can navigate the extended arm through a maze to reach the final point. Now, I have separated the hand using depth threshold. And when I apply vertex shader, it does not attach itself to the hand but, acts on a point in the output window. Such that when my hand comes across that point, it gets distorted, but otherwise stays intact. What approach should I use?
Should I try to generate the mesh from the point cloud like, here,, and then try to manipulate the vertices?
Or, should I use any other approach?