I forgot about a trick we used to use with a hunter in the party when we were going after thespia. Put the hunter pet in the water, the same pool of water that the arcane container is in (that has the karazhan key quest fragment). Miss direct pull thespia to the pet and then own the elementals. I think you still have to look for the storm clouds while she's off on her wild goose chase, but it's one less mob to deal with while you take out the ellys. If you use this method, i would suggest not banishing so you can just kill both while thespia is gone.

Remember your frost and nature resists.

There was a macro floating around the forums like

/assist party1
/targetenemy
/cast Spell

I use it for fights that need add control and it works wonders. I use this for the 2nd and final boss in steam vaults. You're guys will instantly switch to the distiller when it's up. The only problems I had was sometimes the alts would not target the distiller when i expected them to. This had everything to do with the camera positioning. Your guys have to be looking at the active distiller in order to pick it up properly. If your camera is pointed into the ground on the alt character, he might not pick up the distiller as you'd expect. I had to move my clones up closer to the boss and the distiller i was tanking him on and make sure their cameras were adjusted to see both objects on the screen. Once I started doing that this boss became trivial. Just stop blasting when the spell reflect is up.

Use amplify magic for this fight.

One last note on the above macro. If an add appears behind your group sometimes they will target him and not be able to attack it. This is a royal pain in the ass and is the only flaw I can find in that macro.