3ds Max Animation :: Lock Sub-object Face Selection

I have a triangular shape that is against a thin surface. I need to move the pointed end around but I need for the wider end 'face selection' to stay put or be locked in space. The rig was made with bones and skin with constrain and look-at controllers on the bone and nub.
 
I've tried linking verts to point helpers with linked xform and I've tried every kind of contrasting I can find and I just can't get the result I need. My goal is to have the end faces lie on the thin purple wall and be perfectly locked to it so that when I move the point everything else follows but the faces against the wall to be rock solid. 
 
You'll see me move the pointed end around. Then you'll see me select the faces on the end.