I have an '07 X1 pretty much same boat as yours. That piece of the floor is not screwed down, it's just a tight pressed in fit. You should be able to get it out without taking out the center section of the rear seat. But be careful because it fits under the seat.
You should be able to pry up on the front of the floor section with a regular screwdriver or stiff putty knife. As you get the front part up just pull it forward out from under the seat.
Hope this helps.