I think the Brad Pitt idea would work, especially if he were willing to emaciate himself ala Christian Bale in the Machinist. The Fiennes guy looks perfect for Rob. How bout Edward Norton with bleach blond hair for Kretz lol? No idea for Dean just yet.
How about Phillip Seymour Hoffman as Brendan O'Brian? I have no idea what the guy looks like, but for some fucking reason Phillip Seymour Hoffman always ends up in this kind of movie, always as the producer.