I have read through many of Bowjunkie's threads also in hopes of understanding his method. This is my understanding of it:
The fulcrum would be the balance point on your bow hand where the pressure is applied. Usually between your fore finger and middle finger, but will vary depending on the person holding the bow, how pressure is applied, and the shape of the handle. In your picture and the way that grip is shaped, the fulcrum should be pretty close to the center line.
You want to simulate the way you hold your bow and apply pressure onto your tiller tree. A rounded off piece of wood matching the contour of your handle would simulate the forward pressure of your grip. Any imbalance during the draw cycle and at full draw would be evident when setting up the tree this way as Zradix explains.