I got through 8 pages, so there may be another update from the OP.
The issue is not whether your son has something to read, it's that he's ASSIGNED to read for 5 minutes during each class period.
I, too, am an extremely fast reader and was like your son in that I'd fly through books daily. However, if there was an assigned reading period and I didn't have something to read, it was a no brainer to take one of the classroom books. No matter how boring.
The Dictionary is an excellent suggestion, he may also find it boring, but come SAT time, it'll pay off in spades. He should ask the school librarian for advice. Lots of times, if you say I like Lovecraft, Asimov, and Wells, they'll offer some alternatives. Heck, that makes things fun for the librarian. The school librarian loved finding new authors for me-and we'd have great conversations after I'd read those books!
There is no need for you to spend tons of money at the bookstore. Heck, go find out what the reading lists are for high school english and have him get a jump on Frankenstein, Catcher in the Rye, Macbeth, Oedipus Rex and all those books he'll be required to read.
Go for college reading assigments. I had Oedipus assigned in three different college classes in two semesters. Rereading it was not high on my list-but knowing the third time through that the Professor was looking for insights on Creon or Jocasta made me pay more attention to them.
I don't get the 'standing up for his rights' argument. He's been given an assignment-don't complete it, suffer the consequences.
Finally, there are genres of books that I'd dismissed for years. Thought they wouldn't have plot or substance. Surprise, they do! So, in that spirit, encourage him to look through the bookshelves for other books that 'look' interesting.
Suzanne