A family of Microsoft word processing software products for creating web, email, and print documents.
I know this question is really old, but since I had the same issue but figured it out, I thought I would post it here. In your source manager you have a Master list and a Current List. The Current list is the list of references entered while working on this document. In the current list a little check mark appears to the left of a reference. This tells you if the reference has been cited within the document. When you are done (aka not adding any more citations) remove the unchecked references. They will remain on your master list, but won't appear on your bibliography.
Similarly, if there is a reference you use in many different documents you can always pull that into your current list from your master list so you don't have to recreate that reference.