Well, then you will forgive my skepticism, because my experience is that information passed around by birthers through word of mouth tends to be unreliable.
Can you at the very least tell me in which book he talks about this adoption? I could probably find someone in the marketing or OB department (they tend to be lefties) with a copy and I might be able to skim through and find it.
You don't even need to leave your computer desk. You can do text searches of both books at Amazon.
Though I can tell you right now that he doesn't say anything about being adopted in "Dreams From My Father." Because I already checked.