Just tie a length of 1/4" dia. shock cord to the intersection of the two booms, then lead one end back through the forward hole in the top of your daggergoard and tie the ends together near the intersection of the booms. Fiddle with the tension as needed to get the rig to hold your board up or down and to keep the boom forward when runinng before the wind in light air. It is a good rig, simple, dual function.
I make a loop out of #/8 shock cord with a 7 - 8 inch tail. I then tie a 12 - 15 inch 1/8 inch line to the tail. The 1/8 line goes to a small clam cleat on the top of the CB. Pull the line to get enough tension from the shock cord to hold the CB where you want it.