[yodeli]

Jeff, you wrote:

How can one increase the clubhead speed by applying a push action in the later downswing?

I see it like this:
Imagine you are in a center of a rotating merry go round.
Your flying wedges are set, horizontal to the ground: your right forearm is on plane of the rotating merry go round).
You are halfway in the downswing.
Your right elbow bent and in a push condition.

If you stay static in this position, your clubhead travels at the angular speed of the merry go round (this is your body power).
And to your point of view, your whole Power Package is static and ready to be fired as a hitter.
If you now drive with your right arm, your clubhead will travel at the angular speed of the merry go round PLUS the speed of the thrust

As Biomechanics says:

Tour players hit at the bottom to get better compression and distance,produce better ball flight,
switter will smoke it past a swinger or hitter every time.

I confirm from my experience that this is a HUGE difference: a real gain in distance + deadly accuracy.
Really impressive.

The key is to blast the whole power package set in its pushing condition instead of only the left arm.

Also, I'm pretty sure that if your merry go round decelerates before impact, you won't be able to catch up the primary lever assembly with your right arm thrust as it separates from the chest (not a problem in a swing and supposed to work like that), resulting in some kind of strange throwaway feel!