I think I read in Graham Hills autobiography about the time Team Lotus was struggling to finish a second car off for scrutineering. So after the first car was wheeled back, they simply peeled the numbers off and re-presented it with the second cars numbers and no-one new any difference.
Also there was the time when a very successful former driver was running his own team and a young pay driver was struggling to qualify for his race (the old F2 I think). As time was running out during the final session, said young driver returned to the paddock in his car parked up next to the transporter, got out and disappeared into the wagon (fully kitted out still in overalls & helmet) for a couple of minutes, only to return a few minutes later, get into the car and return to the circuit and produce a couple of blistering laps which put him halfway up the grid. said driver then returned again directly to the paddock and back into the transporter. On his emergence no-one commented that he seemed to lose a few inches in height and gain a few pounds in weight and vice versa everytime he went in and out of the vehicle!
