> I don't (yet) need dynamic linking; my current main aim with the .mllib setup is to specify the package dependencies for each plugin in its > own section of the _tags file, and not have a long list of every plugin's dependencies in the main module.

Well, that doesn't quite work: you need to have the ocamlfind packages
passed to the command linking the final executable.

I suppose changing
  <**/puz.*>: ...
to
  <**/puz.*> or <file.*>: ...
could work, as this line seems to pass all the libraries flags.