Hi,
The trick you saw what to be able to sell products after their stock goes to 0.
That's not the case in your example.
Since the book/CD is not printed yet, you can sell as many of them as you want. The more the sell, the more you'll print, and the more margin you'll make on the sales. So I don't see the problem with the stock. You could just put the stock to unlimited and have your customer purchase the products.
You could simply have some text in the name and/or description of the product to tell the customer that it is a pre-sale, and then remove that text once you have the book/CD printed.
That way, you would collect the money directly. And you could just change the status of the orders to shipped when the orders will be shipped in order to notify the customers that they will receive their pre-sale product shortly.