I've scrolled through the entirely of Yoshimitsu's moves list, but I guess I've missed something because I absolutely cannot figure out how to turn him around so that he's facing away from his opponent. The only consistent method I've found of doing this is to do the deathcopter move and fly over the opponent, but it's not very practical.
Here are a few basic, reliable ways to turn Yoshimitsu around so his back is facing the enemy:
66B+K (i.e. while running forward, hit B+K) will do a leaping somersault and end up with your back turned.
66A+K (i.e. while running forward, hit A+K) will turn you around and do nothing else. Make sure you don't hold A+K too long, though, or you'll stab yourself through the stomach, committing seppuku.
The developers removed this aspect of Yoshimitsu in SC5, along with a bunch of other moves.