Julian Monney. Unfortunately the site where there was video seems to have shut down.
I think, without being able to do either of course, that this is probably harder than the slack rope ultimate wheel thing because at least in that you can see where the restoring forces come from and what you could react against even if you would have to have awesome balance and arm strength to do it.
In China Julian and I and a whole bunch of top riders stood together, when he told he would do it. Everybody laughed, cause they couldn’t believe it, and thought it was a joke. As it theoreticly was possible, and Julian is the biggest unicycle talent ever, I didn’t laugh cause I believed he could do so. It took him years, but man I’ve played that video over and over again!
By far the “Best unicycling trick” ever! (or else; go out there and try it with support!)