You will need a character with teleport to do this.
There are two ways (but both require teleport)

First Way
Have the person with teleport stand south of the platform middle, between the council and on the rocks. This will be just before the grass and steps. The person with teleport wil TP onto the steps in front of Rommy. You will get a cut scene. After the cut scene, TP away. Now, have the tank character go in and hit Rommy. The tank can not taunt or ranged attack though. Doing this will cause him to come alone. Rommy should stand at the steps and not move. Have a line of site to the Nictus, and kill him for exp now.

Second Way
Trigger the cutscene, but do not go up the steps. Teleport into Rommy and TP out. The AV's will stay by the stairs, but no duplicate Rommy will spawn. Have a line of sight to the Nictus, kill him.

Going for elite so please coment