Sorry - but don't think you are out of the woods yet. This can cause a blockage which may go on for days. If it were me, I would not give him any food for 24 - 48 hours, until I was sure all the corn was out of his system. Mini's have a extreme tolerance for pain, and will eat as soon as the belly ache temporarily goes away.
Just lots and lots of water, and I also give warm water enemas. WALK WALK WALK.
If the vet gives some pain medication, and the pain comes back as soon as the medication wears off, you have a serious problem. I had one get a blockage, and was able to treat it with IV's and no food. I couldn't afford the surgery, and she luckiily came through fine.
Again, make sure your little guy is clean as a whistle, inside and out, before giving any food at all. Including Hay, grain, grass.
Good luck!!