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My main source of information here is the O'Reilly UML 2.0 book. Its common for an artifact to display a manifestation by adding a relationship between the manifest and a component. For example, in the diagram in the URL the manifestation shows that the jarfile is providing either the server or client component (actually its providing both but thats a whole different discussion). So I think it would be a welcome addition if there were a standard way to setup a <<manifest>> association.
I'm moving this to fixed because the plugin project has evolved since then and as far as I can see this behavior is supported now.