Placeholder

When all else fails.  Something to hold the place until the genuine article arrives.

Cousin to the seatfiller.  Someone who fills (duh) a seat (duh) at an event like the Academy Awards - especially while the true attendees attend to the call of nature.  So when the cameras pan the audience, no empty seats.  There's a whopping metaphor in there somewhere - some day I will suss it out.