I lived in the same box until Monday of this week, so don't feel bad. Go to/ join the Equine Cushings Yahoo group and read the "start here" files (under files) about the emergency diet.
http://pets.groups.yahoo.com/group/EquineCushings/
I started soaking one of our minis hay on Monday and boy am I glad it isn't the big horses hay I have to soak! Princess isn't wild about the diet change, but she is eating it. She was already on a fairly low sugar/low carb feed with rinsed beet pulp and Remission (magnesium and chromium supplement to help prevent founder) , so it may have been less of a change for her. Be sure to read the other basic files too, because you need to pay attention to vitamins and minerals.
Good luck with him. I hope others who have dealt with these issues longer than I have will add their comments.