It's not too much different then old style quad kiting really, you have to gather up the mobs, then get them bunched together (doing circles around them will do this), then you have to out run them far enough so you can actually cast the beam, once the beam hits you gotta resume kiting until you build that distance again.
Things like SoE / Selo's will help with distance as well as getting snare on them (wiz, druid, bard?)
You can also pop all your burns like twincast and that to bump up damage to beam them down faster
If you die a few times don't give up
. You just have to get used to the mobs and how far you need to cast and the beam to hit them hehe