Are you looking for something like diagram partitioning? (http://wiki.eclipse.org/GMF_2.0_New_and_Noteworthy#Basic_support_for_diagram_partitioning)
With this feature you can create "parent" diagra, and open "child" one associated
with selected diagram element by double-clicking on this element.
(like on class-diagram from Ecore example you can double-click on package
and open it's content in a separate GMF editor)