It's also possible via the 'q' action to control what's going to play next. By right-clicking on the stop button -> on end of queue -> uncheck 'use setting only this time' & then going back & selecting the 'stop playing' option on there, when a file is selected as the next play by selecting it in the main playlist & pressing 'q', once that's been played it'll then stop on there (or go to the next playlist item depending on the other playback options).
If it's something that's always wanted on specific items then the separator option might be the better way to do it as there isn't any virtual metadata to link such a behaviour to items as things currently stand with wacup.
-dro