Finger cups are a great way to get powerful launches. With your thumb on the leading edge and two fingers in the "finger cups" you can really give your wing a HEAVE!
I can get 40 feet on a launch (with my 19 oz. XR Combat Wing - a little less with my light weight Zagi THL) using this method of launching... it's easy to install and cost practically nothing!
These "finger cups" are actually sliding cabinet door "finger holes" They also use something similar on the bottom of chair legs to keep them from scratching the floor. They come in plastic or brass and cost about $1.50 for a pack of 4. I used the 3/4" dia. x 3/8" deep brass ones... it's what they had at my local hardware store. The brass ones are really thin and don't add any significant weight.
To install your cups hold up your wing and hold it comfortably with your thumb on the leading edge and your fingers under the nose of the wing. Mark where your pointing finger and index fingers are located. For me this was about 4.75" back from the nose and 2.75" apart (center to center).
After you mark the location of your fingers trace the outside diameter of the finger cups onto your wing. I cut through the tape with an exacto, then used a dremel tool to carve out the foam. I like to make them a tight fit so I have to push them in tight. I used some 5 min. epoxy to secure them. NOTE: I like to install the cups AFTER I have put the tape or covering on the wing, that way the cups help hold the covering on after you press them into place.
One thing I did not like about the cups is the disturbance of airflow this will cause. Zagi's already have penetration limitations and I did not want to add to it. I remedied this by making a tape "flap" over the finger holes. I made the flap out of 2" strapping tape and stuck two pieces together face to face, leaving about 1/2" of the sticky side exposed to stick to the wing just in front of the finger holes. Check out the photos.
Well, this tip will help your launches incredibly and if you are flying electric it will save your fingers from the prop!