I don't think it's Sawyer at all...I mean, it makes a nice twist, but they couldn't have known it was him all along.
Why go through all this just to have Jack operate on Sawyer?
No, I definitely think it's one of them that needs it, and probably Ben.
Why would thay have had to "known it" all along? Or, they could have known it all along. They seem to know a lot.
Also, it's not Juliette because Jack said the x-rays were that of a 40-year old man.
What got me thinking about it is they made a big deal out of Sawyer's age. ("how old are you?" "32...okay, okay. I'm 35." ... then later, "assuming you were telling the truth about your age...").
And, then Ben also says something possibly crytic about Sawyer and death in response to fake-beard-guy: "You know so-and-so wants Ford dead." "Well, he'll just have to wait." ...maybe implying that Sawyer is as good as dead?
I dunno. I think it's Sawyer. I think in the previews they maybe cut it so that it looks like Jack is delivering the bad news to Ben, but in reality is delivering the news to Sawyer.