[Walkin Stummik]

Hey i've got a robot that has two antenna. I've applied a vertex selection modifier right below a flex modifier to make the attena wobble whenever the the head moves. It works great except that the center for the Flex stays in one place even as the Character moves. This makes the antenna flex badly in the opposite direction it normaly would. How do I get the flex center to move with the antenna?
Any help would be appriciated.
Pic below illistrates the problem.