Back when I was a teenager I took an old encyclopedia and painted glue on the outsides of the pages. When it was dry, I took an x-acto knife and sliced a rectangle in the middle of the pages -- it's about 4"x5" and about 2.5" deep.
I just kept it on a shelf and it was never discovered. I still have that book to this day! The binding's a little worn from being used so much, but it still works. I don't really need to stash it like that anymore though, but I do keep it out of sight when I'm not smoking -- just in a drawer or something.