They could market it as Game of Thrones: A Clash of Kings, although the book geeks might not like it.
Although Season 2 will be MOSTLY based on the 2nd book, the creators of the show have said that they will move up a number of chapters from the third book to the 2nd season (much like they moved up a couple of chapters of ACOK to the first season). I'm thinking as the series progress, you will see much more of these happening. I haven't gotten around to reading them but I'm told that a lot of
A Feast of Crows and
A Dance with Dragons happen concurrently with one another so 4th and 5th seasons will be a hodgepodge of two, maybe three books.