Put tank in the middle and make a 3 point joust(or put everyone else on autofolow/shadow on another character and manually run them). Each time a rift pops, move to the next joust point. The adds move slowly and if you get far away enough from the rift they stop spawning(but you'll inevitably have 6 up eventually). You basically need to avoid having too many of the adds near the group, as they cast an AE each that hits for 10-20k and it triggers fairly often.