masked movie, which should be moved by a detected face

Hey there,
it's my first post, so please forgive me, if i oversaw something or made a mistake ;-)

In my Max-kinect-project, i want show a masked movie, which visibility is influenced by the persons z-distance to the kinect (i've done that already) and which position inside that mask is controlled by the faceposition of that person. I use 'Synapse' and Windows 7.

The masked movie should show bit by bit its left side, if the persons head moves to the 'worlds' right side. It should show its right side, if the persons head moves to 'worlds' left side.

My problem is:
How is it possible (is it?) to move the x- and y-position of a movie, while the masking object stays on its position?

Thanks in advance, Mirko