Apply the auto traced layer over the layer you wish to subtract. Change the subtract layer's track matte to "alpha inverted". Select both layers and precompose(shift+cntl+C). Now you have a layer with a hole in it.
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.