The attached patch should define a new extension point for diagrams. This extension point permits to export the current EditPartViewer from the context menu.
I couldn't get the patch to work, did you use the latest code in the git repository? However, by looking at the patch file itself I could figure out what it is you're trying to do. I could add such an extension, but the question for me is will you build and distribute the SVG plug-in yourself? As the plug-in requires so many GMF libraries and it becomes so large it would mean the Archi download would be too big just for one feature.
This functionality is implemented in version 2.7. :-)