Surely with all the effort in faking the paperwork you might as well done it for real?
Not really ~ the only lesson that needs real planning is when you know you are being "observed" because the "observers" want to see the lesson plan and will pick up anything in it that you didn't cover. Of course it is prudent also to ensure, if you are going to try optical illusions etc on your class, that none of the children are epileptic.
A great many teachers are only two pages ahead of the class anyway where they are asked to teach things other than their specialist subjects.