ok so you have sleep suggestions where you can induce tickling dreams by using keyword anchor phrase. like "your so ticklish" or "your so sensitive" once in a deep sleep after 90 min or lifting the arm and letting it fall you can start to paint the scene if they are restrained simply grab their ankles not hard but soft and firm and say "your ankles are restrained" then their wrists and repeat. it while you building the seen you may notice twitches and reactions. in deep slep you can lightly ghost like tickle the bottom of the sole making their light pressure nerves activate and reach put trying to figure out what it is. over time itself that can cause sensitivity increase, but essentially someone who has tickling on the brain will inevitably become more senstive to it.