Treat master sources and source details like places and place details. Then one could cite the combined master source / source detail as the "source" in multiple citations that would effectively be linked together. The citation details would be limited to things like the quality of the "source" for documenting specific facts or notes specific to that use of the "source". The master source could be something like "Louisiana Death Certificates" and the source details would include the specific certificate details. An image of the certificate could be attached to the specific source detail in the master source. Any change made to the master source or the source details would be reflected everywhere that combination was cited.
Alternately, others have proposed some kind of citation linking, rather that simply memorize/copy creating new copies that need to be edited individually.
This is one of the main reasons I've had to resort to extreme splitting of my sources.
More details can be found in this forum post: http://forums.rootsmagic.com/index.php?/topic/17407-master-sources-source-details-citations/