I was thinking, perhaps sprayable lithium grease from the auto parts store would work. It starts out thin and liquid, until the solvent evaporates, and then it thickens up. It would make a godawful mess while trying to spray it past the tiny gap between the ring and the side of the head, but once the grease thickens and the excess is cleaned off, it should work fairly well.
However, as an experienced user of titanium flashlights, I want to say: don't expect the grittiness to go away. Titanium is never truly happy with any lubricant until the lubricant is packed full of little bits of solid material, which acts as a sliding agent to keep the titanium parts from rubbing directly. The grittiness you feel now is producing little titanium shavings which will eventually cause the lubricant to work better, and cleaning them all out and replacing them with fresh grease will just cause the grittiness to return. I fell into this trap and put a lot of premature wear on the threads of some of my lights until I understood what was really happening. The only time titanium lube really needs to be changed is if the titanium parts were covered with machining debris, but since Jetbeam polishes their titanium lights, that is fairly unlikely. Generally speaking, it's better to incrementally add new lube to replace old lube that was washed away, instead of intentionally removing all the old lube and replacing it all at once.