Well, when Palka is in the lineup, Davidson is on the bench as a backup 1B/3B and when Palka is on the bench you have a backup corner OF. So you assume a 4-man bench would be: backup catcher, one of Palka/Davidson, hopefully Yolmer (IF), and then a 4th OF who can play CF. They have been going with a short bench the last 3-4 years though and only carrying 3 bench players.
Edit: also keep in mind that it doesn't need to be a straight platoon. You could see Eloy, Abreu, whoever is at 3B, whoever is in RF get some rest at the DH spot.