Earlier this week, I had actually thought of this as a possibility, but didn't post about it since I thought that if Ignatieff wants both Cauchon and Le Prohon to run, having Cauchon in Outremont and Le Prohon in Jeanne--Le Ber is much more electorally efficient. Indeed, it currently appears that Outremont will be a tougher battle than Jeanne--Le Ber. Since Cauchon is a former Outremont MP, and is in any case much better known than Le Prohon, the logical choice would have been to nominate Cauchon in Outremont.
It looks like the reason why we now have it the other way around is to avoid embarrassing Coderre too much. Ignatieff is attempting to cut the pie in half by saying, "Denis, you can put your preferred candidate in Outremont, but you cannot prevent Martin from running as a Liberal." Unfortunately, this may achieve the "worst" of both worlds: Coderre is still disavowed since Cauchon is allowed back, and the Liberals may have lost Outremont in the process. (I put 'worst' in quotes since that's from Ignatieff's perspective - I personally have no problem with embarrassing Coderre to punish him for overreaching.)