At a point in the Thieve's Guild questline, Mercer Frey accompanies you to a dungeon. He has no dialogue other than one unimportant option, so you cannot ask him to stop following you. After several tries, I decided that the dungeon included in the quest is too hard to clear, so I'd like to level up before continuing. However, since Mercer won't stop following me, he continues to screw up my play style (as a sneak Illusion-type character), alerting people of my presence by opening doors that I've closed, standing in line-of-sight, etc.
He's very annoying. Without the aid of a mod, is there a console command or other way to tell him to buzz off while not breaking the quest when I chose to return to it?