The way that I find works for me is to ensure that the opponent is overextended so that his balance is broken already before applying the kote-gaeshi so that you aren't just relying on the wrist-turn (and is generally less painful). Trying to kote-gaeshi someone with a strong wrist in a balanced position is risky. Just my 2 cents.
Our dojo seems to rely upon this heavily, and many (including myself) are building resistance to static kote-gaeshi, enough so that you can almost walk out of it.
I say thumb in between pinky-ring finger knuckles and other fingers wrapped tightly around meat of the hand with a dynamic technique is the best way for this technique.