You CAN build AND search for a 2009, and have been able to for some time.
To build, go here and select 2008 Malibu, enter your zip, and submit. Then when on that first page, go into the URL address and where you see "...yes&subModelId=67&year=2008&y=...", change the 2008 to 2009. The page will update, and you'll see the models and prices and can continue from there.
http://www.chevrolet.com/byo/build.cv?year=2008&make=Chevrolet&makeId=001&model=&modelId=
Same for searching inventory. Go to the Find a Vehicle page, enter 2008 Malibu information, and then when you get to the search results, change the 2008 in "...&year=2008&model=..." to 2009 and hit enter. Bingo. Now you have 2009 inventory.
^^With the inventory, you can also extend the range it searches, in mileage range and number of cars shown in the URL.