Fixing dupligroup library links

I have some object groups from one file (source) linked to dupligroups in another file (target). I had to change the name of the subdirectory containing the source file, and the name of the source file itself, so the links in the target file broke (as expected; even relative file paths wouldn’t have helped with the renamed file/directory). So now when I open the target I get the error message stating missing data, and all the dupligroups are just empties (empty empties that is).

What is the best way to fix this and restore all the dupligroups? I had two ideas that both failed:

Idea 1 (failed):
-Use file/External Data/Find Missing Files

But “Find Missing Files” does not seem to work in this situation; pointing it towards the directory with the renamed .blend file does nothing, and it will not let me select the renamed .blend file either.

Idea 2 (failed):
-Go to the outliner
-Select “Datablocks” in the pulldown
-Expand the “Library/lib” item
-Change the “File Path” field to reflect the new subdirectory/filename

After doing this the dupligroups are still just (empty) empties. Is the problem that the empties are no longer linking to the groups? I’m not sure how to tell.

Any insight or ideas would be appreciated. Thank you.

(I hope Tech Support is the right forum for this question)