I also have a NF pony who is rather over weight and has been tested for EMS. I rang Saracen and they were so helpful. They told me to try Shape-Up which is a feed balancer but it is designed for EMS and lami ponies. I have been feeding it for about 6 weeks and the difference in him is amazing...
I have also been using this method for my fat pony. I rang Saracen Horse Feeds and they recommend that i try him with a big bucket of chopped oat straw - i use their slim chaff, alongside some soaked hay and i believe that it has really worked. he always has something to eat but is loosing...