Associating .pdf files to existing Endnote references

I have been maintaining a library for years using different solutions (ProCite, Endnote, Bookends, etc.). I have recently gone back to Endnote X6, which has successfully imported all my references from my previous solution, but without the .pdf attachments. The .pdfs are stored in a directory and are sequentially numbered to correspond with the “Label” field in each Endnote reference of my library.

My question is, how can I associate (import?) my .pdf files with existing Endnote references? Is there an AppleScript that can do it? I have about 4000 references in my library; I need to associate about half of those with .pdfs I have stored in an external folder.

I know about the Import feature, which will create new references for each imported .pdf. But that’s not what I’m looking for (that would essentailly duplicate my library, and I would lose many notes associated with several of my existing references). 

One trick is to copy the Label field to the URL field and edit the field to include the info that makes it “live”.  This avoids having to do anything with the actual PDFs.