Vidaloco I'm sure I've heard people on here saying that you should do hill exercises to help with a locking stifle. Apparently it helps the supporting muscles somehow.
Here's what my horse bible says for treatment:
Treatment, regardless of severity, is relatively simple. In young, out-of-condition horses, feed and exercise will take care of it in most cases, unless the horse is genetically or conformationally predisposed to the condition. In a horse that must be stalled for a prolonged period, deep bedding and/or shoeing with raised heels reduces the liklihood of upward fixation of the patella.
In those horses in which ready release does not come, backing the animal will usually bring about release. In more stubborn cases, it has been suggested that the release can be attained by manually pushing the patella upware. The guy who can do this can also leap tall buildings in a single bound; it has never worked for me. (that's out of the book, not my words -- really!)