I'm still not sure what people mean by this displacement mask.

There's already an image applied to the displacement node in this case.   Is that the displacement mask?

This is the image of the settings.  For this one I altered the displacement image, changing to flat gray the areas where displacement isn't wanted.

 http://www.imagebam.com/image/1fb73b166957767

It removes the displacement, but there's seams between the chest (where there is no displacement) and shoulders.