RichFaces has the notion of autoupdate - a list of "always render" id's, that
are rendered for every ajax request.
A quick, naive implementation could be as simple as:
void jsf.ajax.addAlwaysRender(String id)
and then every jsf.ajax.request would have the "id" appended to the render list.
This would be trivial to implement.
The use case for this is actually a special case for component authors - while a
page author can manually add id's to the render list, component authors can't.