I think there is a yahoo group called equine copd or something like that. Many on it have had success using spirulina, which is a type of seaweed.

For soaking the hay, it shouldn't just be wetted or sprayed, but actually soaked for 12-24 hours so that all the spores expand (so they cannot be inhaled). Most people only wet it or soak it for a couple hours. The horse at my barn with COPD gets soaked hay cubes twice a day (rather than hay) and he does get grass hay at night that has been soaking for 24 hours. She has two big bucket type things with a spigot on the bottom, so that it soaks and then they just empty the spigot and the horse eats the wet hay right out of the bucket.

Also, while he's having his flareup, just making sure he does not overheat, I am not sure where you are located, but here in Minnesota it has been very hot and humid, which doesn't help anything!

Good luck. Sometimes it can be managed, I will think good thoughts for your friend's horse. I have an Irish horse as well, he's 26 years old and my best friend.