DOCBOOK-APPS: indexing an entire set

Hi all,

I've successfully made indexes for my books. Now I want to combine some books 
in a set - is there no way of making an index for the entire set? The spec 
says that <index> can't be a child of <set>.

I know there is <setindex>, but that doesn't let me benefit from the 
automated indexing provided by Norm's XSL style sheets?

I'm using xml-books (4.1.2) with Saxon and Norms style sheets.

/claus