Interactive Image Panning within a Mask

Hey guys thanks for the help so far. The last piece to the puzzle for me is figuring out how to scroll a movie clip within a mask. I’m currently working with the script taken from the Interactive Image Panning tutorial on this site as a base. Right now the script references the entire Stage area for scrolling the image whereas I want this to happen just within a mask. How do I set this up. Here is where I have the script right now:

this.onMouseMove = function() { constrainedMove(Work_placeholder, 4, 1); }; function constrainedMove(target:MovieClip, speed:Number, dir:Number) { var mousePercent:Number = _xmouse/Stage.height; var mSpeed:Number; if (dir == 1) { mSpeed = 1-mousePercent; } else { mSpeed = mousePercent; } target.destY = Math.round(-((target._height-Stage.height)mSpeed)); target.onEnterFrame = function() { if (target._y == target.destY) { delete target.onEnterFrame; } else { target._y += Math.ceil((target.destY-target._y)(speed/100));}}; } ps. the instance name of my mask is Work_mask (movie clip)