Need to lock subobject face selection of skinned mesh to position in space

[RobH2]

Hi, I've spent two days trying to figure this out, have done probably 25 tutorials and read for hours and I can't get the result I'm after.

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 constrating 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. 

Is it even possible to achieve this? See my video that's attached. You'll see me move the pointed end around. Then you'll see me select the faces on the end. Those are the ones that I need to lock in space or constrain to the thin box to the left.

http://nvision.s463.sureserver.com/public/lock-subobject.mp4

(FYI: just  tested this link. IE is OK but Chrome doesn't seem to like it.)

[RobH2]

Ah-ha...looks like the ability to 'edit' a post times out. 

Anyway, here is a bit more info. I'm able to solve part of my problem but not all of it. I hope some of you guru's can help me.

In the image below I have a purple box on the left and a red sphere on the right. The image is not really my rig, it's just a simplified shot to help explain what I'm doing. The video in the post above is the real model.

I need to attach the left-hand verts of the pink cylinder to the purple box surface and then attach the righ-hand verts of the cylinder to the red ball. They need to stick and not move around or slide. I need to be able to move the red ball around and have the cylinder follow it and squash. The purple plane will remain stationary. 

I figured out that with envelopes and weight table I and lock the left verts of the cylinder to the box, that works. But, when I now try to lock the right-hand cylinder verts to the ball or to a bone nub and then the ball so the ball can drive the rig, it breaks. I'm half way there. 

So, how can I attach both ends and have the ball drive the position of the right-hand side of the cylinder while allowing squash?