Tracking position in After Effects CS5?

I'm doing a commercial as a school project, and the idea is that I'm placing a persons mouth on a stuffed animal and having it talk.

I have two footage clips: one of the boy saying his lines, and the other of the stuffed animal being held up.

I've masked around the boys mouth and feathered it, but now I have to have it's position match that of the stuffed animal's mouth (it is being held, and it's position is constantly shifting).

I've already gone through and used the "Tracker" to track the motion of the stuffed animal's mouth, but I get confused because it turns those keyframes into "motion tracker" keyframes, and I don't know how to link those keyframes to the position of the boy's mouth.

Any help would be appreciated!