Chaim, there is indeed a 20-second video of Joe and Randy riding their invisible ponies onto the stage in Houston, November 1976. If only I knew how to link or post it here. It's on a closed (members only) Facebook page, so I can't just link to it.

Or you can just watch the whole concert. It's a good one. Joe and Randy are wearing matching Criteria Recording Studios t-shirts. Too cute, those two.