This is a suggestion that should work but I haven't tried it. On the LOTC, there is a small allen head screw that secures the contact plunger to the metal button (under the rubber switch cap). If you remove the spring and then the screw and contact plunger, you might be able to place a spacer between the contact plunger and button. The thickness of this spacer will be the amount that you stand the cap away from the flashlight body. If you use the SureFire lanyard ring, this spacer wouldn't need to be very thick and I believe the screw is long enough to still connect the contact plunger to the button.
I don't know if I have explained this clearly. If the spacer is too thick, you may end up exposing the O-ring when you turn the cap to the "lock out" position. I don't have one of those lanyard rings or I could try this myself and report my findings.
You could also get some spectra fishing line that is the thickness of a thick thread but stronger than necessary and splice a loop on the body, forward of the O-ring. I believe you will find that you can still go to constant on with the cap.
- Don