How to scale a rectangle along its length in one direction while keeping the stroke fixed in after effects? I am animating a rectangle with a stroke and would like to it scale up and down along its length in only one direction while keeping the stroke fixed.

I have managed to either keep the stroke fixed but not scale it in one direction, or to scale it in one direction but not keep the stroke fixed. :( 

I have learned that in order keep the stroke fixed I can create a shape layer and edit the "size" rather then the scale. The problem is that I can't get it to "scale" in one direction now. (I know while editing the scale I can move the anchor point to the side I would like to scale from but while editing the size moving the anchor point has no effect and I haven't been able to find a solution.

Any suggestions? :) Thanks!!
In this situation I would right-click on the path options in your rectangle and choose "convert to Bezier".  Then instead of adjusting the scale, I would keyframe the path, and change the shape of the path in this way.