Man... its very sad to know that a brother smoker was jailed because of this wonderful plant we love so much... if at least he could smoke in there... the life there would be far more bearable... anyway... if you said he did read all Castanedas books (that would be my first suggestion) and likes metaphysics and such, i would greatly suggest this one:

Beyond the Physical - Science and Occultism

You could print it for him (it would be cheaper than buying a book)... its a very good book that would give him a lot to think about while there.
Also, there is one called Journeys Out of the Body, by Robert Monroe... he will have a lot of free time to practice it, and when he succeed he wild be able to get out the jail for a while (even if only a part of him...).
And send to him my best wishes, and when i were toking and remember of him i will toke for him... :thumbsup: