Does it have to be books? Or will magazines do? I know that's a lot of magazines but if he has a hobby or interest, he could get a ways toward this goals by reading several magazines about it. Other thoughts: books about sports heroes, if he's interested in that, and always biographies. You might find books related to the TV shows he watches. Or books like "How things work" might interest him. Or "How to" books, like how to build a pirate ship or Computers for Dummies or even textbooks. And, is the requirement that he finish the book or just read the required number of pages? If he doesn't have to finish, he might get 100 pages from one book and 150 from another. Not an ideal way to read as most books are designed to be read from beginning to end but if it works, it works.
I don't know if that seems helpful, but just looking at it from a different persepective than "read this long book" might give him ideas. I hope you find some things that work.
