So... you are wanting a true tactical type switch? One that doesn't click at all, but works like the Inova X series or Surefire G2? A true tactical is press for momentary, twist for constant on.
I've never tried it, but it seems like that would be relatively easy to make with a little effort. Just ditch the clickie component entirely. I know with the cheap Chinese ($5 or less) 3xAAA lights, the switchs often come apart and en up being 'tactical' on accident.
If you are wanting it to work like a Maglite switch (press for momentary, click for on) that is going to be more trouble. You'll probably have to scavenge a switch that works like you want, then modify, cut, sand and house it to fit in the Fenix. More trouble than it's worth in my opinion.