Is there some way to do this that i'm not seeing other than methodically subduing damn near everyone on the map? I've had multiple runs go over an hour before i'm spotted by one of his enforcers.

The best approach i've even come up with is slowly peeling off 1 of his guys at a time and choking them out... but it takes some absolutely insane patience and you have to start stuffing bodies in places where you simply hope they don't get discovered (i jam a lot of people in that tiny room in the garage).

I'm guessing once i get down to maybe 1-2 guards with him i might be able to set off some decoy explosion and then hit him with the lethal syringe?

I would have to say this must be, by far, the toughest challenge in the game.

I haven't done it my self, but the way that i've seen it done is by remote breach charge and propane tank.

@slatterg:

Yup. The Life Extinguisher makes SA trivial.

I saw something like that in a video...am I right in thinking that you can set off a breaching charge a fair distance from a propane tank or fire extinguisher and the breaching charge will somehow set off the tank?

@ohbabes:

Just slap the breaching charge right on or next to the tank/extinguisher and detonate it when the target walks by. If you place the charge instead of throwing it (hold L1 and R1 and press Triangle to place), it doesn't count as a suspicious action, so you can do it right out in the open. If somebody walks by the charge, they'll pick it up and bring it back to a weapons box, but they'll leave the extinguisher/tank in position and you have two charges, so it's not a big deal. Just be careful not to accidentally kill any guards with the explosion; the range is deceptively large.

OK, i pulled it off with just a propane tank.

I really wish there were a clean way to pull this one off. It feels pretty cheap to have to do it that way.