If Joe wasn't in such a funk this would be the time for the Mauer at 3rd experiment. But the way things have been going with him messing with a new position seems like a bad idea. Unfortunate.
Before Pinto was sent down, I suggested trying Mauer in corner OF spots as a means to get Pinto more DH reps, keep Morales in the lineup at 1B, and rest Willingham. Maybe take his mind off hitting for a bit.
3B is quite a bit more stressful defensively, so probably not recommended (although it could take his mind off hitting even more!).
I do wish they weren't quite so quick to give him a full-time position -- he could have easily been subbing at 3B and the OF all season. I know both he and the team might feel a little weird to have their "star" player bouncing around, and they all feel like he could become a defensive asset once he settles in at 1B, but I don't like the idea of going straight to the far end of the defensive spectrum full-time.