One of the main things Tim Cook did when Jobs hired him in the late 90's to do the day-to-day running of the company (i.e micromanagement) was that he drastically reduced the amount of computers Apple kept in stock. Because of this, for the last few years Apple has had less than a week's worth of stock in storage at any given time.
Thus I don't believe any significant cache of custom order machines is going to fit inside of this stock situation. Commonly this kind of inventory management is called "Just-in-time".