Putting a horse in cold water will bring down the swelling, but the cold cold water could also kill other healthy tissue as well. So heading it off at the pass like that is a myth. I'm not really sure what drugs can be administered, as I've never delt with an episode of founder before.
Have you ever read the books by James Herriot, the vet?
In of the stories they treated a foundering pony by putting him in a creek, several times a day. I can't remember how long they soaked, but it wasn't constant.
Becky