First, I too am interested in results of using a glidecam 4000 with the hvx, so any replies would be greatly appreciated.
Second, based on my experience with a stickypod and a GL2, mounting an HVX would be pretty scary. There would be no question that you would have to devise some sort of extra straps and supports, both to keep the stickypod down to the car and to keep the hvx stable once its mounted (this may only be an issue when driving 70 on bumpy roads, which is how i used the stickypod most often). That being said, i think the stickypod can be an excellent starting point for a solid car rig which will be much cheaper than professional alternatives. The work to convert it will be well worth it.