External links between documents

Is there a way in DT to link two documents without inserting hyperlinked text into either?

I can do this with Hook, but if I can do the same in DT and have the links and backlinks show in the inspector, it would be better. My particular use is for client contracts that are derived either from a standard precedent or a contract written for another client. It’s useful if returning to a contract to quickly see its provenance, and equally if it’s been used as the basis of any others, but obviously I can’t clutter client B’s contract with a hyperlink to client A’s!

One possibility is to use custom metadata (requires the Pro or Server edition), see Preferences > Data. E.g. the Item Link data type or also a rich text field containing links.