Board Thread:Skyrim/@comment-101.112.60.147-20140129051316/@comment-90.203.255.199-20140322141030

You can't perform the Sacrament on Sithis or the Night Mother, as they aren't living, physical beings. The Dragonborn is the Listener, and he could perform the Sacrament on himself, as shown in the final DB quest: Astrid did it on herself.