SPG, I have no idea if this helped or was just coincidence, but we started DS playing violin when he was 5. It was very hard for him and he struggled with it, got frustrated, cried, and generally didn't like it. But we kept plugging along and now he plays well, not amazing, but well. When he started K and he would start to sound frustrated with the other kids for not learning as fast, I would say, "remember how frustrated you get playing violin because it is hard. that is how the other kids feel about learning to read." That seemed to make a lightbulb go off for him.
So I guess one approach is to find something, even just one thing, that is truly challenging for him and make sure he gets to really struggle. For DS, I think that built in some empathy.
I would also make sure that he is getting things he really likes at preschool. Even if he is bored some of the time, that really should not be his primary experience. If it is, then another preschool with a different curriculum may be your answer.
