Only do this if you have sign-off from higher-ups. Otherwise you risk someone seeing this and going straight to IT with “I’ve been hacked!”. They will determine that it was you who messed with the computer and refer the situation to HR, who is not likely to care that you had good motives when violating corporate security policies. In a worst case scenario, you could actually be prosecuted for this.
That being said, the easiest thing is to just place a sticky note on their keyboard. In my experience, just knowing that someone caught them in a mistake can be enough motivation for many people.