I usually can get my heirs to be rather good at anything by just using them to supress rebels that wander through your lands sometimes. My faction heir never moved from the capital city but for one time to squash a rebel army and he has 5 or 6 stars and great Managment and Influence.

mainly I think that Generals and Gov's are pretty easy to train to be good - the problem isn't the training, it's the using them where they count the most because you have a lot less than you did in MTW.