"Reverse" Body Tracking

Hi there,

I'm trying to use the body tracking feature, except in "reverse."

What I mean is, where the default template allows you to set a sprite etc. to track shoulders or centre of a body image in a camera view, what I want is to be able to have the camera video itself (cropped / masked face in this instance) snap or track to the face area of a photo or a video; similarly to these:

Dancing Bee

Dancing Granny

Dancing Cheerleader

I've looked and looked and I'm really struggling to put something like this together without using the fairly convoluted tweening system.

Is this doable? I've played with the settings for ages and done many a Google search but I'm having little luck finding a clear solution.

Many thanks!