This is a trick question right??? I've been around the block and read your posts in other forums...
Horizontal hinging is the natural full roll hinge action for a swinger. To let it happen, it requires a mandatory flat left wrist into and through impact all the way into follow through (both arms straight).
In the backswing, you will turn the left hand palm to the plane, and on the downswing you will feel a left hand karate chop motion back down the plane. You will feel your left wrist uncock at your release point (when the clubhead and butt of the club switch ends), and without any effort on your part, then next thing you will feel is the the sweet spot of the clubface and the right hand paddlewheel motion rolling your left hand into impact.
Clubs are designed to roll around the sweetspot. This is sensed through the #3 pressure point and the right hand is simply executing it's paddlewheel motion as the right arm straightens. Let me emphasize here, the right hand is passive. This is all just a consequence of the right arm straightening as the club nears impact. Let it continue it's roll into the finish swivel. If you have kept your left wrist flat through all of this, you will find your left hand palm facing up as the left arm collapses into the finish.
All of this requires that there is never any thrusting or pushing of the right arm, only right arm extensor action on the left arm. The wrists stay relatively loose. Otherwise you end up fighting an angled hinge and then you will have to force the roll. The role of the right wrist is to remain bent, level, and passive. The role of the #3 pressure point on your right index finger is to aim the sweet spot at the inside quadrant of ball and sense acceleration.
One more thing while I'm on the subject. The left hand is the clubface. Monitor it's position throughout the swing.
Hope that helps, if you are still having difficulty letting it go, let us know. I'll bring in the big guns...