I haven't contributed in awhile so here goes.
I'm not sure if this has been posted before, as a mage Ice Block just before Kael'thas finishes casting his gravity lapse spell. When you comes out of Ice Block, you'll be able to run around on the ground the entire time, and not take any damage from the rays that usually target you in the air. You do still need to run away from the orbs though.
I haven't fully tested it yet either, but it happened last run.
Just a heads up and thanks.