Vetrolin has a very good line of products for horse care. There is one product that is a spray on non-rinse conditioner for manes and tails. Dang it all though I can't think of the name of it at this moment. I know it has Silicone as a main ingredient and intended for manes and tails only. I did however find it to be extremely useful also for helping to free up the lug nuts on a blown tire wheel on my pick-up a few years back.
Something I learned from a friend who had a QH mare that she competed in open jumping and Dressage with was using the only the bottom blade of a set of clipper blades to trim and thin her horse's mane. Doing about a one inch section at a time with the cutting edge of the blade toward the horse's neck tease up to the crest and then with a very quick downward tug cut the mane hairs to the desired length. I tried it with my mare and it did present a tidy, pulled mane look.