Stringhalt, tying up, and high fat diets

Hi all, I'm a newbie here too. Just hit me that I should ask about Stringhalt, as my horse was diagnosed with this a month ago.

Stringhalt is really a symptom of possibly many things. My 16 year-old appy raises his left hind really high when he walks. Typically is an injury to the lateral extensor tendon that affects the leg lifting reflex, but may have underlying neurological causes that weaken the muscle. One of these underlying issues could be EPSM--equine polysaccharide storage myopathy, which keeps horses from processing carbohydrates to glucose. A 2005 study found that 86% of draft horses have this.

So here's my question...Does anyone have any experience with moving horses to high fat diets, particularly easy keepers? I've been reading about high fat diets for horses and have just switched Foster to a 20% fat feed (Progressive Nutrition's Pro Advantage High Fat diet). He's an easy keeper and currently on stall rest (moving into arena soon I hope) so he only gets 2 lbs of grain per day and 4 flakes of 20-30% alfalfa/grass. This wouldn't give him an overall 20% fat, but the vet at Progressive Nutrition was worried about weight gain--and yes that is a problem even at this low feed level. If you haven't had an Appy, believe it! Swear the guy can gain 50 pounds in a week.

Thanks to anyone that has more info on this!
Here's more info on the diet:
http://www.draftresource.com/EPSM/Draft_EPSM_DIets.html

http://www.bevet.com/Neuromuscular%20Diseases.htm (scroll down to treatment strategies)

http://www.flyingchanges.com/htmls/2006/May06_PSS.html

And a Youtube video of a horse with stringhalt--Foster's isn't as bad as this video, but the good news is that this horse was cured.

http://www.youtube.com/watch?v=gVaQqQp7OhQ

No pics of my baby yet, have to move them off the old computer.