Well I seesaw to get horses up into the bridle....But I don't go a "western pleasure" headset, I just take up the seesaw, then just hold contact and my horses know to stay on the vertical, or draw their chins down if need be. I can do it with one hand too, and just pick up the reins and they will drop their heads. But when they are just learning, they get lateral flexion, then we graduate to vertical flexion.
Here's a little Clinton Anderson spew for ya. At a stand still, bring your horses head either left or right to your stirrup, then use the outside rein to try and bring their head back to center WITHOUT them raising their head even a fraction. I cannot tell you how frustrating this can be, but I also can't tell you how impressive the results are. My reining mare can now do it at all gaits.
Pssh.I didn't pick up the wrong lead
It's called a counter canter...
...A very advanced maneuver.