I've done it without removing the bumper. Just pull the bumper corner out and down, you can then get a screwdriver onto the screw at a funny angle.
I've got to remove the rear bar to sort out the tread plate anyways - http://www.aulro.com/afvb/discovery-...w-secured.html
You do not have to remove the bumper to access the screw. It is not obscured to that extent, get down on your knees and you can see it. If the bumper is hiding it it is adjusted wrong / Bent. I see you have to remove yours anyway, but thought I would clear that up for others. :)
Cheers Scott