I agree that there probably needs to be subject matter that is a bit more dynamic. Part of Seuss' charm is his prose, which is going to be lost on a kid learning to read english as a second language. I would think it would be really boring. Comic books are a good idea. (get some of those golden age ones where the chinese are portrayed in the worst stereotype possible) "Look, this is what we round eyes think of you."

But seriously, I think comics are a good idea. Maybe there are some english translations of fairy tales he was told as a kid? So he could learn to read the story in a whole new language. Well, hopefully they have an illustrated book of something like that.
If not, alice's adventures in wonderland/through the looking glass is always a real trip. It's weird enough for anyone. There is prose in some parts he may not be into, (although I think the walrus and the carpenter is a wonderful little poem), but for the most part, the narrative is totally wacky.
Sendak's work is good, too, but you know.. it's where the wild things are.. the plot is kind of basic and might be too young for him.
Im still seeing the movie when it comes out.