It was supposed to be Nick Johnson, but he's... well, Nick Johnson. Looking at their recent lineups, it looks like they've been rotating the regulars in and out of the DH spot when and where necessary, and particularly getting good mileage out of catching Cervelli and DHing Posada. I imagine this move allows them to stabilize the DH spot with another switch-hitter with power, particularly with the short porch in New York, who can also start a time or two a week at first base and the corner outfield spots, if they think his legs can handle it.