You shouldn't try to put tracks on a device in a library playlist (but maybe I misunderstand what you're asking).
If you want MB to coordinate files between the library and the device, use a playlist for syncing:
*create a playlist with the tracks (from the library) that you want to sync
*set up your auto-sync settings to use ONLY that playlist (or playlists), not "Music Library"
*check the box for "delete tracks not in auto-sync list"
Then use the "synchronize" button whenever you want to apply updates. Files which have changed in the library will be updated, files no longer on the playlist will be removed, and files added to the playlist will be added to the device. All other files will be left alone.