Question about facial clusters

Hi all.
I'm trying to write an script and i am having several problems so i hope someone can help me.
The main idea of the script is to create some clusters to move the geometry of an object something like the Cluster-o-matic. I can not use the Linked_XForm modifier for two reasons.
a) It pushes a new Linked_XForm modifier for each cluster i create and i want only one modifier.
b) If i have a Morpher modifier below the Linked_XForm the cluster do not follow the vertex where i created it, it remains static when i change the value of any of the morpher's channels.

Because of this problems i'm writing my own solution.
I have put a dummy on the vertexes i want to control and had put them a transform modifier targeted with the morpher modifier of the object so each time the morpher changes the dummy follows the position of its vertex. I have also put a sphere object at the same position of the dummy to act as the cluster and it also moves each time the vertex moves.
I have put another transform modifier to the vertexes i want to control to follow its cluster.

The problem comes now. If i change the value of any of the morpher's channels the dummy and the cluster move to the new position of the vertex (that's ok) but the vertex does not move correctly because the movement of the cluster causes also the movement of the vertex again and after that the movement of the vertex causes again the movement of the cluster and the movement of the cluster causes again the movement of the vertex and the movement of the.......You now what i mean, right?

I have no idea how to avoid this redundancy, any idea?

If someone knows any other way to solve the cluster's problem any idea is welcome.

Thanks to all of you in advance.