Use a page action with a view-id of /* in pages.xml.
I actually tried that first of all and to my surprise it did not work. Now encouraged by your response I revisited that idea. I just found that at a later place in our gigantic pages.xml there indeed already was a view-id="/*". This entry shadowed my initial attempt. It seems that later entries in the pages.xml overrides earlier ones. (This raises the question: Should really seam start from a redundant pages.xml. I think not. But this is another story)