We do lots of reading aloud. That is a big help. My 10YO DS always says, “Can’t we just read a little more? You always stop at the best parts.” 😉 That is, of course, by design.
Reading aloud, trading off reading (you read a page, he reads a page), audio books, reading a book followed by a movie day, and low-key book clubs with friends help to encourage a kids to read and enjoy more difficult books.
That said, I do make sure I choose books of the child’s interest (there’s no sense giving my 4th grader a biography of Harriet Tubman – that’s better as an audio book or a family-read aloud; and there’s no use giving my 14YO son Anne of Green Gables – it will be torture for him. He did enjoy it as an audio book, though).
Perhaps choose a book below his reading level that suits his interests (check the book lists on this site). Also choose another to do as a read-aloud – we’ve done The Secret Garden, Charlotte’s Web, A Midsummer Night’s Dream, Black Beauty, A Christmas Carol, Macbeth (and many others with dad at bedtime). Read just a few pages each day, at most a chapter, and savor the book over several weeks or months. Allow him the time to develop a love of the storyline, the characters, the story.
My kids still have “twaddle” on their bookcase, but much less than they had four years ago. Take your time, don’t force the issue and turn him off from reading altogether. He’ll get there!