I'd like to think that exemplarity can function in a similar way, especially if it is allusive rather than ad hoc. Admittedly, it has been 4 or 5 years since I read that book, so I may be attributing to H. ideas of intertextuality that are not his.

Is the Hostius Quadra exemplum (Nat. Quaest. 1.16) ad hoc? I don't think I've seen it elsewhere, though the vita of Horace has a similar story.