Thought I'd start a thread for this, as there isn't one.
First, the trick:
http://youtu.be/Mz3TRPbilPU
https://www.youtube.com/watch?v=NbSwWHEeZO4
Second, Akimoto-san told me "it's only possible with luck"!
Third, I missed this when it was posted last week, but caught it today. It's not a Merry-go-round, but it does have a MGR spin in it, which suggests there are other variations waiting to be discovered.
https://instagram.com/p/BDsV9fJpw3S/