Why not stick post-it notes on instruments?
My PPL instructor once confessed to me that he lost one of his suction cups which he used to give his IMC students "instrument failures". He was very embarassed at having to use one suction cup and one post-it to cover the instruments. I suggested to him that if he used two post-its, the students wouldn't know of the existence of suction cups, and so there would be no need for him to feel silly.
As far as I know, he took my advice and never replaced his lost suction cup!
FFF
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