Brandon Backe added almost a full win with his bat in 2008
Unfortunately he pretty much was a moot point overall if you take into account the fact he was a -0.8 on the mound. Roy added a 0.29 WAR with his bat. Caveat: The league average wOBA used to construct these values was .172, or well below league average. So this these aren't apples to apples, but interesting none the less.