I couldn't get your video to work, but I'd avoid trying to stretch tubular tires off the rim: they'll twist so the base tape is on the outside and the base tape will start to separate from the tire. As Ex Pres notes, used tubular rims are abundantly available. It doesn't matter if they're out of round, dented, or otherwise unusable on the road; for stretching they'll work just fine and such derelict rims can often be had for free.