Hackers help: Hemnes Bookshelf Height Extension?

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We’ve recently inherited quite a large number of books and are looking to turn our formal living room into a library. Love the look of the HEMNES bookshelves but our ceilings are tall and there is about 2ft of unused space above them (we will need to use every last inch of space). Has anyone heard of a good option for an extension that is the same depth? Our quote for custom shelving is over 8k 🙁