wierd situation

Figure out what his best resources are for help and reps for new position.  Sounds like it's not necessarily the HC.  Often, assistant coaches are willing to work with kids before and after practices.  It may need to be with a local facility/academy or a private instructor or a willing ex-player or combination of the above. 

Just from the limited amount of info provided, there seems to be good news...

1.  A MIF can usually move to most other positions fairly easily and have success.

2.  Coach recognized and put him in another position instead of just letting him fall down the depth chart - must see value.

As your player progresses, this becomes a fairly common obstacle.  If he wants it bad enough, he'll do what it takes to overcome.  Having the MIF experience will help him regardless of what position he lands on next.  It is quite common for MIFs to be turned into OF's transitioning from HS to college, for example.

Best wishes and let us know how things progress.

How's his bat? Offensive production usually drives positioning more than a little, even up the middle. Best 7-8 bats tend to find a spot and that can indirectly impact positioning too. Tell him to keep his head up and keep competing on all fronts and don't let anything get him discouraged!

Sometimes players find some of the assistant coaches to be more approachable. When my son had an issue with the head coach he went to an assistant who was a former teacher and his middle school football coach. They had a very good relationship.