Tricky roto/ stabilize job

i’ve got a distance shot, a person moving from the far left of the background to the right side of the picture margin… there’s a camera pan, the person does not stay in the middle of the picture…
what i’m trying to accomplish based on this footage is to get rid of all the background (spent some time with the roto work:) and then pin the person to the middle of the screen and keep him at steady size (i know this means quality loss), eventually i want this to look like the actor’s doing a dry run on the very spot …
the difficult part for me is how to track the entire person in this clip… the person is moving constantly - walking actually -, so i figured a rectangular x spline shape might do the job (tracking transition and scale only) … sad thing is though that because of the movement i’d have to manually set keyframes for the position and the size of the tracking x spline shape… which would cause a lot of inaccuracy i think… i would be forced to try to understand the movement of camera and person to set the proper keyframes… (btw would it be useful in this case to set “link to track” to “none”?)
am i totally wrong about the way i try to approach this job? any ideas how i could improve this workflow?.. maybe use the roto shapes for stabilization?
help needed … thanks
btw. wasn’t there a separate mocha pro section at creative cow’s?

well thanks for your quick reply martin …
i was hoping i’d get some answers to my initial questions though … anyone?
or is the description of my problem too vague?

When tracking people it’s usually best to got with the most planar object: The torso. Often I will use the head if it’s not turning too much. Of course, it depends on how far away they are.
When tracking something moving towards the camera, it’s actually best to start with the largest scale first and track from that point.

Which initial questions would those be?
If you can share a clip that would be better.