I know only of adding them manually into the sql database. Use SQL Server management studio to do this. Add new rows to the recordings table, with the right path to your video files.
Next time if you delete or upgrade your database, make a backup first, so you can restore the recording table, it's more easy than hacking into it with SQL management studio. ;-)
hmm, maybe I will write a little tool, which will add a folder to the DB.
The problem is, that it did not happen after a DB-upgrade. I just have restarted the TVserver because it was freezed. After that my recordings-table was deleted.