I do know how he did it. :)
He rolls to his back, then grabs his feet, pulls them up as far as possible, and rolls over to his side. Then when he stretches back out again, it's at a 90 or so degree angle from where he used to be. He can turn himself in circles this way.
Clever, isn't he?
I would also like to report that Jonathan just entertained himself perfectly happily for 25 minutes.
Big, big, big smiles. :)