From a dojo down in the south of Japan some time ago. I just saw this going on and filmed it. I never learned how to do it — when I asked to be shown how to fold mine the same way, they said it was a special technique which they wouldn't teach "visitors".
Update: I've put the original movie on the site if you want to see it in all its glory. I needed to tidy it up a bit before letting YouTube's compression squash it (file is about 1.5Mb).