I tried one on a G2 (non-LOTC) with a Cree drop-in module, and it works except the domed pushbutton of the switch is too long. It would need to be cut and shortened to fit properly.
A hacksaw and a file would make short work of fitting it to the G2. The button has a groove and O-ring to seat it in the inner plastic retaining ring. Cutting it right at the groove would work, then round the sharp edge with a file. You'll also need to shorten the bolt that holds the McC2S together, either separately or by sawing it at the same time assembled.
As far as the resistance/level selection, it depends on the driver being used. A Wiz or GD boost/buck will behave much differently from a DB or NG buck or boost only. The Wiz/GD will require a much lower resistance (5-10 ohms) to decrease the brightness a comparable amount, and won't even light at higher resistances. For a boost or buck only, a general rule of thumb is that 10-15 ohms will give more of a med level, 20-25 a mid-lo, and 30 and up will give low levels of output. In most cases the resistor will force the driver out of regulation but increase runtime.
These were out of stock for a long time, but I see Wayne has a few in stock now. Surprisingly they don't seems as popular as I would have thought, but obviously there hasn't been much word spread. I stocked up on a couple when I saw them available, and I suggest getting them while you can.