The reason to increase the billow at the top of the sail is that, when flying certain tricks, a tight sail is a bad thing. So, to allow more pressure to stay in the top part of your sail, simply tie the two leading edges together. Tie one end to the left LE just below the top bridle point, and the other to the right LE, again, just below the top bridle point. The Trickline and Curl the S ail. Now for the blasphemous bit - the trickline.
First thing is to remove all three rubber end caps from the spine and two LE spars.
Next, tie a single knot as far from the sail with each pair of tension strings. Then, find a piece of flying line that will give you 50 to 51 inches of line including a loop at each end. Larkshead one end to the left knot, the other to the right. So, tighten the sail and pull each knot through it's corresponding arrow nock. One simple trickline and a tight sail.