Have animated character react to real world elements

Ok, so I've watched the video on mixing animation with reality, and understand the basics of motion tracking in AE.  I have a scenario where my real-world subject has a character on her shoulder, and because of the nature of her movements, slight shoulder dips, head turns and all, I'm looking to make the character respond more naturally to its environment.  Meaning, if she dips her shoulder a bit, he would respond to that gravitational pull a bit, etc.  

Using the physics tutorial, I guess I could create an imaginary floor that the character stands on, and animate that floor alongside a png sequence in CH?  Because the movements are so subtle and random, it feels like I would have to animate like 3 frames at a time to get it to sync up.  That's crazy.

I'm just wondering if there is any advice on a workflow, and how you would go about accomplishing something like this.  Thank you so much!