Wouldn't the most braindead way to do it be to just use different items and swap them out when you reach the page they can be used? Like, have a greyed-out sword to sit in your inventory when you can't use it, with no script (so it says "Item cannot be used here" if you click on it) and then just use a different itemstate in the page script to swap to the colored-in version when you reach a page it can be used?
I suppose that would require a lot of pages with script, and careful thought. But the scripting itself would be stupid easy. Unless I missed something.