The factory rear sway bar is all you need and it will NOT limit the amount of flex you have the way an Anti-Rock WILL. The rear sway bar is soft enough that you can manipulate it with your hand but will still offer some stability when disconnected up front. Here is a shot of Moby at a full flex WITH coil overs. Please notice that the limiting straps are taught and that the swaybar itself is warped a bit from the extreme twist.
To this day, I run factory front and rear sway bars on both my EVO DTD JK's.