Hi Cawshun
Most of us find it very difficult to impart information to people who don't want to hear it, never mind trained to view anything critical of the WT as satanic.
I wouldn't put the book in their mailbox if I were you. They'd guess its from you and no amount of denying will convince them otherwise. They'll just think you're lying and be even more suspicious of you.
The beauty of Captives of a Concept is that it keeps its points simple. In fact the logical points it makes about the WT are easy to remember and to casually to drop into a conversation.
Don Cameron also advises to use the method of "playing dumb". In other words, ask questions, pretend you want to know the answers to certain bible questions or WT history, then get them to do the research in the guise of finding the answers for you. Really they'll be teaching themselves. He outlines this in the book and gives suggestions on the type of questions to ask.
Its a bit of role-playing. You be the pupil and let them be the teachers. Only in reality the roles are reversed and YOU are the teacher. They just don't realise that.