Fixing water-warped hardwood flooring?

One of my housemates put his air conditioner in the window so that it tilted into the room. The first time it rained, the rainwater funnelled through the A/C and left a large, 1/2-inch deep puddle over much of his bedroom floor. This caused the floorboards, which are old and about 2in. wide, to warp up (I don't think the wood warped, really--the boards just swelled and pushed themselves up and over one another, like this - _/\_/\_ ).

We let the wood dry out, and the swelling has gone down, but the boards are still not lying flat. Is there a way to push them back into place?