Ex post facto law and the War Crimes Act of 1996?

I ran across several articles on the Administration’s response to the Supreme court’s Hamdan ruling today, and not being a lawyer, found myself confused. Here’s a few representative articles:
Detainee abuse charges feared
Bush administration seeks shield from 1996 War Crimes Act

U.S. seeks to circumvent War Crimes Act

'96 law could lead to war crime charges
Geneva violations were criminalized

To my non-legal mind, the strategy of making a crime legal after the fact, sounds a lot like ex post facto law, which Wikipedia assures me is not permitted under Article I section 9 of the constitution.
So how are they going to get around that detail?

-GQ only please. I’d like to get an answer.

An Ex Post Facto law is one that criminalizes an action after it occurs.

What is being discussed is decriminalizing actions after they occur, which is Constitutionally acceptable. In fact, the Constitution expressly gives the President the power to pardon, by which he could effectively acheive the same end by granting a blanket pardon.