Haven't seen anyone else mention this, but it was a very surprising and amusing outcome. If you choose to expose Mortimer during his speech in the members-only section to the White Glove Society regarding his cannibalism, after he tries to run away, if you manage to attack him (he runs fast, but you can use VATS to freeze time, target and hit him) before he exits the door, everyone in the dining room will turn hostile on him, and what's especially amusing is that the members of the White Glove Society with canes will take them out and start to collectively mob and beat the crap out of Mortimer with their canes. In my case, they massively beat on him until he was able to scurry to a corner of the room where they didn't follow him, and as he cowered, I went there and finished the job. Got his formal wear and top hat, too.