I tried using plain duct like suggested in the OP, but the vive's curved surface didn't lend very well to that. However, foam is great for molding into curves, so I cut out a chunk of the foam from the vive packaging, cut out a slot for the leap motion, and duct taped it all together.
Even with just an approximated position, the mount has worked quite well. The only issue that one might encounter with this kind of thing is your hands being slightly further forwards than if other mounts were used, although I suppose I wouldn't know as I haven't used other mounts.