Loctite polymerizes in the presence of metal ions, which is how it hardens in the screw threads but not in the plastic bottle. Guess what else solidifies in the presence of (polyvalent) metal ions? Solutions of soluble silicates: waterglass!
Suppose waterglass by itself in a screw thread doesn’t harden because the metal surface doesn’t spontaneously oxidize just because it’s wet? Even if galvanic corrosion isn’t a viable source of cations, maybe the surface can be induced to oxidize with some kind of nasty oxidizing anions. For example, maybe you can use sodium chloride, potassium sulfate, ammonium acetate, or some crossbreed of them to provoke oxidation of iron, brass, or aluminum. Only a tiny amount of oxidation is necessary, only enough iron ions to precipitate the silicate, which itself should be present in only the minimal quantity required to achieve the desired bond strength.
Another interesting possibility I haven’t tried is baking soda. Waterglass hardens in seconds upon contact with carbonic acid, and baking soda releases carbonic acid upon being heated above 50°, leaving behind its conjugate base, the more basic soda ash. Perhaps this reaction could solidify waterglass in a thread if you heat the whole assembly above 50°? I suspect that the carbonic acid solidifies the waterglass by dropping the pH, and if that’s the case, it will not work.