DOCBOOK-APPS: htmlhelp: merged chm's

I need to generate multiple chm files from DocBook source, merged in several
master files. Are there any plans to support OBJECT/param[@name='Merge'] in
the htmlhelp stylesheet?

I thought of using <set> for master files and <book> for subordinate chms,
but there are some other problems: first, I need merging at levels deeper
than 1 (nested <set>s?), and second, the <set> itself needs an introductory
section, which is not allowed by DTD.

Can anybody advise something?

Thanks a lot
Tatiana