What is the best way to set up ReplaceKeys on someone's computer?

Wait until your target steps away from their desk. Launch ReplaceKeys with command-line options so no configuration window appears -- for example: replacekeys.exe e i 0. Now every time they type the letter "e", an "i" appears instead. Watch as they slowly realize their typing looks completely wrong but cannot figure out why. For extra subtlety, use a longer frequency so it only happens occasionally.