x33,
Don't worry! Luxlover has got you covered....
So far, the best method I have found to guarantee keeping an L4 or any similar type of light in lock-out mode before storing it, is to hold the switch button in and unscrew the bezel a "pinch" until the light goes out, and then unscrew it a "hair" more. No matter what happens in a pocket, the light cannot come on.
As for the loose fitting threads, did you buy the McE2S switch with a tailcap, or place the switch inside an existing tailcap? May I assume that your o-ring is applying enough pressure on the inside of the tailcap? Is there any reason that the tailcap should not snugly thread on the body? You may want to investigate this matter further, since I have many SF lights with various tailcap sizes, and they all fit snugly. In the meantime, if you want to place a small strip of teflon doping tape to keep everything secure, make sure that it doesn't migrate and cover the leading edge of the battery tube where the pc board of the switch makes contact with it. Good luck!