Remove the headrest, on the side that there is not a headrest adjust button there is a little button in the plastic bezel that faces the outside of the seat, use a flashlight to find it and a small flat blade screwdriver to push it in. This allows the headrest to come completely out of the seat. You will need to have the seat leaned way back to do it. Once I had it out, I clamped it by the legs to the side of the bench with two c-clamps and piece of 5/8" Baltic birch plywood. Clamp it so the headrest is almost against the bench, and make sure the plywood on the front side of the clamps is almost up to the headrest as well. Then I stuck a smaller piece of the same plywood in the jaws of the seat clamp to make a fulcrum point. I used a 3' pipe as the lever, and another piece of plywood between the headrest and the pipe to spread the load on the headrest. Then it's archimedes to the rescue, it took 1.5 people pushing to get it moving. We did one side first, in basically three increments to get the amount of bend right, then used that as a template to match the other one too. Go slowly, and make sure you are bending it squarely. We got a little off and it was easy enough to shift the pipe over to the side that was underbent to square it up again. It's a little time consuming because you have to keep installing removing the headrest to get the right amount of bend, but it's easier to go a little farther than to realize you have gone too far.
The arrangement looked like this:
The result is this, this is the passenger side in what is now the all the way down position.