I don't know what they are called, but I've seen a few cars with an attachment dooferiser wotsit that prevents the belt "tongue" going all the way back up to the door pillar. It's about 9 or 10 inches long. Doesn't affect the operation of the belt. It just means that the tongue is that much nearer to you and you don't have to thrutch back and twist as much to reach the thing.
Some knowledgable soul will know what they are called and/or put up a link ?