I'm on the Planar Prison quest, and I'm trying to find out if there's some way I can free the thralls without killing any of them. I know it's not necessary, I just want to be able to make this a quick and painless battle. Any ideas?

I've not tried it and I don't know if it will work but I'd suggest using maze or imprisonment spells and when you're able to 'disarm' the neck-thingies, then cast freedom in the areas that you used maze. Its an idea and hopefully it will work. Just remember where you casted maze.

That's a really good idea GFORCE, but I don't think it will make for a quick and painless battle...aren't there like 10 thralls to maze/imprison? That'll take some time. (rest to reload spells)

Flesh to stone maybe, don't know if it'll work

Just walk by them invisibly, kill the master-thrall ( i think) ....
Drop the control-orb in the fire and you have happy alive and kicking thralls :D

I tried that, but I can only have a couple of people in my party go all the way to the Master Thrall while totally invisible - and those people can't stand up to him and the Air Elementals and the wyvern all at once.