I don't see an issue with having Mauer DH more and giving Sano time at 1B. First, Mauer is not that great defensively and 2nd I don't know how much that lessens the concussion risk (has a 1B ever received a concussion playing the field?) but DH should be safer in that regard than playing 1B. In my view I would prefer Plouffe play the majority of time at 3B, Sano at 1B and Mauer DH.