The passenger seat should fold fully flat: take a look behind it down by the end of the runners and you'll see two catches. Pull these towards you and push the seat back forward and it goes completely down. You'll need to move the seat fully back and the back of the seat base as low as it can go to allow the headrest to miss the glovebox. Once down you can the move it forward a bit to wedge it.
I notice that the original poster said power seats
. I don't think the fold-flat business is possible with a powered passenger seat. In addition (and perhaps things have changed since we bought ours in 2014), the fold-flat passenger seat was an option.