It seems more natural to have Hermione take an Unbreakable Vow to seek vengeance on Narcissa's killer (ideally with qualifying clauses). This, in principle, would seem attractive to Lucius even or especially if he can't reconsider his theory about Dumbledore (or any of his other beliefs). And I vaguely feel Lucius would worry less about Hermione tricking him than if Harry/Voldemort took the Vow. In any case, this approach to vengeance seems directly related to the trade Lucius publicly declared he would make in chapter 80.
This suggestion might work better coming from Draco's snake-Patronus. They might even get away with adding some lawyer's conditions then. Sadly, it sounds like Harry couldn't signal Draco unobtrusively unless he slips away somehow (or, I guess, casts Expecto Patronum into his Invisibility Cloak while muffling the sound). But the time-turner could work here. I was going to say that even a brief disappearance might make L. Malfoy suspicious. But if LM sees him as Voldemort, that would make faking a Patronus intuitively unlikely.
EDIT: New discussion thread here.
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. With two chapters recently the previous thread has very quickly reached 500 comments. The latest chapter as of 17th March 2012 is Ch. 79.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author's Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven, eight, nine, ten.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: