Note that this only works with the mobile robots, not turrets. There is an option to do this on the top floor of the Belltower building (which you access fairly late in the game). When you first reach this floor through the elevator, there is a locked door on your immediate right. Hack in and then use/hack the security terminal. Here you can turn the Robot onto "Enemies" and it will eventually start attacking the guards and unlock the achievement.
This requires a few Praxis points to unlock the Robot hack option. You can always save first then reload after getting the achievement to both save Praxis points and/or not kill anyone (not sure if it invalidates the Pacifist approach or not).