There is actually a chemical that you can put on the windsheilds to mask it off. I'm not sure what its called , but it looks like blue "white-out" . You paint it on the windows, let it dry, then paint over it. After you're done painting it , it just peels off of the windows. Check a well stocked hobby store.
Another thing to do is to remove the window from the model.
Another thing to do is to remove the window from the model.