Thanks for the comment guys
JHY, as you can see from this pic (plug is at the bottom left) my theory about the "lone plug" is the right one. Let's examine the facts: the Space Station was finished and dressed on all sides, since it's revolving constantly in front of the camera (it had to be).
Now, if you're filming the front of the model, you'll never see the back and vice-versa of course. The front plug (fully dressed) served as the rear plug. All they had to do was: move the model and now attach the front to the stand and place the front plug to the back, light it with red and voilà!
The mounting plate that we see is not really flush with the module (the pic seems to show that, but that's an optical illusion, it's recessed but not by much...maybe 1/4 inch max, which could explain one of my other theory: the back of the landing bay can be removed; but I'll have to confirm that). Another challenge when building this model is that the front is different than the back. If both rings had been built, there wouldn't had to remove anything from anywhere
...just changing the lighting of the landing bay, that's all.