The best method that I have found for rearing is to "bait" them into the behavior, then when they rear up, grab their front legs and walk/run them backward as fast as you can until they almost tip over. It helps to do this in a fairly open area. I have never had to do this twice with a mini, because they learn pretty quick that keeping their feet on the ground is a good thing. They don't like to be that much "out of control". I have had minis that would rear at anything they didn't like: standing, blanketing, etc. Once I did this with them, the rearing was over with....for good. They have never attempted it since.
However, obviously this only works with minis and not bigger horses where you couldn't reach their front legs. And you have to be careful that you put them down before they go over backwards, because you can't control what happens then. It could be physically damaging to them.
I would also not advocate this if you are a fairly new horseman. Get somebody experienced to do it.
Whatever you do, don't "feel bad for getting in to him". This is aggressive behavior and he is trying to test the limits. If you cave now, he has decided that he is herd boss. He may be "little", but he is still about 300 lbs. of horseflesh. He is not a newborn human baby. I treat my minis just like I treat my big horses. They are not "fragile".