it is impossible to get to 60 in one playthrough
It may be possible with the BDtS DLC. In the second building (the one with the prox mines around it) the Rocket Drones from the second floor will respawn, as long as you leave an enemy or two alive on the ground floor.
EDIT: There is also a save/reload exploit where you step off the elevator during the rescue of Liara, but that could take a while.
