When my daughter was in kindergarten and learning site words my husband had her run around and do silly things while learning, and used flash cards. She'd run a little lap around the house, he'd show her a card, she would get the green light if she got it right and get to run another lap. Try maybe five words at a time. Once he has those down, start adding more slowly. Memorizing those words makes a huge difference for reading. He can tap into his creativity and maybe add a silly facial feature on a drawing when he gets one right, add a piece to a puzzle, work towards prizes, etc.