The American percussionist Ed Saindon (1953 -) developed The Fulcrum grip some time during the previuos decade. It is based on the Burton grip but is characterized by giving the mallets, controlled by the fingers, freedom to move in the hand. Ed wanted to create a grip that gave the mallets the possibility to be controlled by the fingers in the same way as when playing with only one mallet in each hand where one can use the fulcrum principle from e.g. snare drum playing.
The loose grip of the Fulcrum grip makes it difficult to apply to standard rattan or wooden shaft mallets. Therefore the shafts are wrapped with racket tape to increase friction, both between shafts, and fingers and shafts, and increase shaft diameter, and also to dampen the clicking that occurs when the moving shafts hit each other in the hand. In the December 2008 issue of Percussive Notes there is an article called The Fulcrum Grip by Ed Saindon that gives a detailed introduction to the grip. At the following adress there is a video with Ed playing and demonstrating his grip: http://www.youtube.com/watch?v=uOPiaGrQJZo.
Below are two images of the grip at the interval of a fourth. However, the mallets here do not have tape wrapped shafts.