My first instrument was piano and, while an Abba band I had joined transitioned to fully live (with me on bass), I played the part of Benny. There were backing tracks and so I did about 3 months of miming the piano parts. It was utterly soul destroying.
Being an ex-pianist, I was able to make a pretty good fist of miming but was always checking out the crowd for people who had sussed out what I was doing. Good money but a hideous experience.