I have a mini stud colt who does this same stuff and the only way to stop him completely is to give him a pacifier of sorts, which is also a lead rope. He has his own lead rope we use around the barn because if I am walking and have to stop for some reason or another he will trying to nip and chew on everything, and all the horses from his bloodline have done the same thing, there is no breaking some of them. The lead rope works wonders and I have not created any bad habits out of letting him chew on it, the only thing it did do was stop him from chewing on me!
You know how to make a miniature horse even smaller? Leave them in the dryer a little longer!
"Don't ever regret something that once made you smile"