Yeah, got TWO tickets for mine until I gave in and put mine on... got them at work; when I quit that job I'm taking the plate off.
If the screws are spinning, then it means the two metal clamps (can't remember the proper terminology) have come off the bumper. You could probably pull it off without much effort, in that case.
All you should have to do is remove the two screws under the plate housing, and it comes off.