Step 1: Make a length of Full Persian that has the end that you want to split having the 'open-V' facing outward. In this picture it's the vertical rings.

Step 2: Add 2 open rings to the end of the chain, to the outside of the other vertical rings. They should go through the same (horizontal) eye as the 2 center, rightmost vertical rings. There should now be 4 vertical rings - you're going to use these to make the 2 new branches.

Step 3: Put 2 horizontal rings through one of the vertical rings you just added, and the vertical ring directly adjacent to it. The new rings should go to the outside of the horizontal rings from the original FP chain.

Step 4: Put 2 vertical rings through the eye formed by the rings you just added and the end horizontal rings from the original FP chain. The new rings should go to the inside of the previous vertical rings.

Step 5: Continue the new branch in the standard FP method.

Step 6: Go back to the second branch, and add 2 horizontal rings to the lonesome vertical rings who had to watch their two friends get attended to first. Poor little fellas.

Step 7: Add 2 vertical rings through the eye formed by the rings you just added and the end horizontal rings from the original FP chain. The new rings should go between the two (heretofore neglected) vertical rings.

Step 8: Continue the rest of the new branch in standard FP fashion.