Manualy setting "Similar Movies"

[stephend]

I know that when the system sees the same name in moves it creates a box for "Similar Movies" I love that feature. However I am not aware of a way to manualy set up similar movies. Example I have 3 movies that are all remakes of each other. "I am Legend", "Omega Man" & "Last man on earth". Is there a way I can set up the similar movies for them?