Wes Dooley (
http://www.wesdooley.com/aea/Modular...ne_Stands.html) manufactures a handy little mike hanger for $10. The mike cable becomes the weight bearer for the mike. The mike's holder screws onto the mike hanger. I use a stereo bar, to control position and separation of the mikes, and run my omni mikes in an X-Y position, but you could also use ORTF. The cables are suspended from structural elements on the ceiling. Because they hang straight down, I adjust the mikes once the cables are settled in place. They never move after that.
It isn't the prettiest thing I've ever seen, but it works darn well. And don't kid yourself, there's no such thing as a true omni mike. They all exhibit directional characteristics, and it's more than enough to make a great stereo recording.
Good luck!
John