First, a disclaimer, I am not an unschooler.
But, I think I may have something of value to offer. I would drop the "100 easy lessons" bit. I like what everyone else has suggested but would add one more thing. Oral Games. The point of these is to boost phonemic awareness skills. Once phonemic awareness skills are strong, then the child can read when they decide they want to know how. These games can be done in the car and stopped if he isn't in the mood for a car game.
Examples:
The basic Alphabet hunt. My kids love this. Start with A -- who is the first that can find something that begins with the /a/ sound (we do the traditional sound OR the letter--so if they get to F and my non reader comes up with a word that starts with PH but still sounds like /f/ we count it).
Swap outs. Start simple: if I were to change the /c/ (say the sound, not the letter) in cat to a /p/ what would I get. Do this will all sound positions (beginning, middle, last).
Turtle talk: this can be like a secret code. Say a word very slowly (one sound at a time) like you would do to sound out a word. Your son will decipher this by squishing the sounds back together and saying it back to you. Then, reverse positions--he does turtle talk and you decipher. This works both on segmenting and blending skills.
Rhyming games. With younger kids we just see how many rhymes we can make, but if this seems silly to him, play the concentration game. . . when I was a kid we started this by saying "concentration, concentration is the game, keep the rhythm, or you'll be out of the game. . . . such as rhymes. . . such as cat and hat. . . such as mouse/louse ) etc. We used to play with all sorts of topics --countries, presidents, names, etc. My dd and her friend do this game too, but they start it out a bit differently. You aren't allowed to repeat or go off beat.
Also, when you are reading make sure to take time for poetry, rhymes, etc.
If you need more information about phonemic awareness and/or games to reinforce the skills, check out "reading reflex" from the library. It is meant for you, not him.
Amy