Hi David, Happy new year.
You can do that with a placeholder video file - just find a small/empty videoclip and create copies of it with the movie names you want (like "Dead Calm (1989).avi"), and put them all in some folder that you add to AutoImport. Then you can import them and tag them as any other file, do Get Movie/TV Info, add a poster, etc.
A better option using a bit more disk space is to download and import the actual movie trailers instead of using the same placeholder clip, and tag them with MovieSubType=Trailer plus any other tagging needed for your views/smartlists. The advantage is that you can then double-click these files in MC and see the actual trailer
There are several ways to download trailers:
https://www.makeuseof.com/tag/hdtrailers-download-free-movie-trailersIt should even be possible to directly import a movie trailer URL from youtube (which wouldn't use any disk storage), but that doesn't work very well with MC. Also, youtube direct URLs have an expiration timestamp, so they might stop working.