The files in the database are referenced by the filename. For an audio file you could create a custom cue sheet (it would be indexed as a separate library file), but a cue sheet does not work with video files.
A workaround would be to create an alternative file path on the OS level. If the file is on a network share you can mount the location as a new drive letter or if the file is local you can use the NTFS junction point feature or create a new virtual drive letter by running a SUBST command (for example, you can have a .bat file in the Startup folder that runs a SUBST command automatically).
The sidecar file may cause a problem if you have Auto-Import set to monitor changes. I have not recently tested if MC can automatically update metadata when only the sidecar file has changed, but if it can, you may need to change the auto-import and/or sidecar settings. Personally I export my video metadata periodically to a few mpl files (one for each root location) and have the sidecar system disabled.
EDIT
I don't know if a sidecar file even stores any playback properties data. I think it is limited to those library fields that are actually set to "write file tags".