You can achieve it (with a small trick). You need to follow the hierarchy as shown in the image below
The expected hierarchy is
Package
->Diagram
->Element
->->Diagram
->->->Element
Now the trick, when you enable the Diagram under Package->Element, you wouldn't have an option to enable Element again, to work around this, enable the "Element" under (Package->Diagram) cut and paste the place holder (element>.....Element->Diagram)
Have exported my template (RTF) for your reference, you can import it and try to apply on your Verify System package) https://www.dropbox.com/s/b9y9jo4xk0yq2zf/SampleRTFTemplate.rtf