Unfortunately that is the only grounding point Ford recommends. Now they also have one behind the rear seats where the rear power access is at too. It use to be under the rear window but I'd say they had some complaints with where it was and they moved it. The green circle is where the ground point is in the pillar that Ryan referred too. You might be able to get away with just pulling the top of the lower panel back to access it instead of removing the whole panel.
Maybe it's only on some options but all the Utility's I've worked on since the power point was moved to behind the rear seats has had a ground post. It's just a simple metal bracket that's bolted in where the rear brace comes down to tie in by the passenger rear seat mount. It comes up and then does a 90 and then has a stud in the center of it. I don't have a picture unfortunately.
It is visible, it would be in front of the foam even with the rear seat bolts on the passenger side. I usually have to bend it out of the way a little to get the seat back in because the feet want to get caught in it.
I went back looking for that ground stud, removed the forward cargo floor section again, short of carving up the foam filler and/or removing the rear passenger seat base I can't find evidence of a ground stud.
Which leads me to another question- does anyone know if the rear seats can be modified to tumble forward like the retail explorer seats?
Glad you found the rear seat bracket ground stud. No, their is no way to make them tilt forward unless you unbolt the rear and side of the seats every time. The front mounting brackets are the only thing that's the same on the seats. The rear mounting brackets are completely different. The Explorers with the tilt seats have strikers in the floor that the seats latch too. You would have to get the Explorer seats and the strikers. I'm not sure how the outer strikers mount but in order to mount the center ones the metal plate that's under the seats would have to be removed. This means that you would loose part of the rear bracing that gives the Utility its 75mph rear end crash rating.