If the rear is anything like the front, the wiper arm attaches to a splined shaft on the wiper motor. I think there's a plastic cover/cap over the spot where the wiper arm bolts to the wiper motor shaft. Remove the cover, loosen the nut that holds the arm, then you can adjust the arm. The only sucky part is that the increments on the spline might move the arm too much.
ETA: just looked at mine, ^ those directions will do what you want. Make sure to loosen the nut quite a bit, and that you reseat the arm such that you don't crush any of the splines.