My main thought is to wonder what kind of help he'd like? At 4 I'd expect that he might have an opinion on what'd help him. Maybe if you make several suggestions and see what he likes the sound of? One thing we used to do when DS was wanting to read but suffering frustration was to read alternate sentences of a very familiar story. That way he got a lot of support from memory; and once he'd had enough of that, I'd just read the rest of the story to him. No need to push. A refrain at that point was also "I'll read it, and you tell me the words I don't know". Often, even though he could sound out words, it interrupted the flow too much and he'd rather just be able to appeal to me whenever he wanted. I went along with it, and his phonics ability is still great. So at least for my DS, following his lead has worked very well.
I was amused to see on his classroom wall a display of all the children's reasons why it was a good thing to be able to read (mostly recording why they want to learn, but it was nicely worded not to exclude those who already can). My DS's contribution was "So that when nobody wants to read you a story you can read it yourself." Now everyone thinks I'm a cruel parent who forced my child to learn to read by being unwilling to read to him :-O
