Placeholder titles?

Does anyone have a suggestion or solution o creating a placeholder title for a movie that isn't in your library?
To save space, especially w my 4k discs, I don't want to keep them on my server. But I'd like to have them appear in my library, and basically say "it's on the shelf, dude."
I know I can add a title and then delete it, but eventually the library gets cleaned and they disappear.