Using previous endnotes/references from earlier in the document

How can I use an earlier numbered endnote in Word 2007, again? Example, I am on endnote reference 20 (if I start a new one) but endnote reference 12 refers to a books that I need to reference. As this books is referenced many times in the main document, I need a way of refering to it in the end note without having to repeat the name of the book again and again.