I played it a bit today and just held the Vita with my left hand (thumb over Sony, pinky along the bottom edge, index along the top edge and the other two straight along the back) and used my right index finger on the screen. I didn't have a problem with it that way and it was easy to shake the Vita to collect sun/coins.
Yeah, I did something similar. It's just a bit too bulky and heavy, though, and leads quickly to wrist strain.
Maybe I'm just too weak.
Edit: Actually, I was holding it towards the middle, thumb on the bottom and first two fingers on the top around the camera. Your way is better with regards to strain, but feels a bit unbalanced.