A suggestion that may make the whole experience easier and more accurate. An issue with Leap Motion is that if there are obstacles around you, you don't have enough space to move your hands. Also if I'm not mistaken the tracking seems to be better in the look-up position when the module is sitting on the desk facing up instead in front of the headset.
So, what I suggest would be an option to use the Leap Motion with FI in the facing-up orientation. The module will sit on the desk in front of the user. Then, the artificial hands will appear all the time in front of us where-ever we look and you have to reach some centimeters out.That way the camera can easily also identify a rotating thumb-pointer finger gesture and may be possible to implement that for rotating knobs. I suppose that it shouldn't be difficult to implement in FI though Dan is the expert to say if its possible or not.