Yes, my friend could, and often did, stretch his thumb *backwards* (across the back of his hand) to hook it on his pinky? He would also demonstrate his ability to bend all his fingers backwards to touch the back of his wrist.
Congratulations on the asynchronous twiddling. I keep asking people to try, and no one has demonstrated the gift, you are blessed. Perhaps you could upload an mpeg of a command performance for us?