how to link to diagram in model documents

[Glassboy]

This is exactly what virtual documents are used for.
And using your "Detail" is what I was discussing about, because this is what your proposal was.

That's why I would like to have answered the question instead of giving other Solutions instead.
First I want to have a answer to my Problem, second, maybe I am interessted in other Solutions or Workarounds
avoiding useless time to discuss.

And now I am back at my starting question:

Is it possible to link diagrams to packages?

I don't quite grasp the context of your question  Inside a <<master  document>> package you can have <model document>> elements that contain packages from anywhere in you model.  As long as your template selects Diagram features then why do you need to copy the diagram to other locations to achieve your result?