I would also love to know if there is a way to modify the anchor point of a shape.
You may also find this (as of yet unreleased) motion tracking mini-tutorial I've made to be helpful. (It's bundled with another mini-tutorial on alpha masks, but the motion tracking one will be the one you'll want to look at for this particular topic.)
I am researching around and intuitively I would use OPENNI tracker to track my hand and then hook up the motion to the width and height dimensions but, because I don't have a Kinect compatible with the plugin, before I buy it I would like to know if there is a better way, and even if this method can be successful.
to change the anchor point of a shape you can use the FFGLPanSpinZoom actor (spin ctrl x and spin ctrl y). It is not a real anchor point but could simulate it.
This plugin doesn't come with a fresh install of Isadora. You'll need to download the TroikaTronix FFGL plugins from our plugin page and install them if you want to use them. Personally, I use FFGLPanSpinZoom all the time because it's more convenient than using both a Zoomer actor + Panner actor + Spinner actor.