Alternate CSS stylesheets.

I currently use the following XSL fragment to include a css stylesheet
in the resulting html documents:

---------------------------------------------------------------------
<?xml version='1.0'?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:fo="http://www.w3.org/1999/XSL/Format"
                version="1.0">
  <xsl:param name="html.stylesheet"
       select="'/home/gavron/devel/docbook/tests/css-dir/flb.css'"/>
</xsl:stylesheet>
----------------------------------------------------------------------

I proceed to generate the html document via a:

$ xmlto -vv -m ../fragment.xsl -o ../html-dir html docfile.xml

Would anyone know whether I can use the same strategy to specify
alternate css stylesheets that I can switch to on the fly while browsing
the html document?

Or do I need to specify the alternate CSS style sheets in the prolog of
each DocBook/XML document?

At this point I modify the XSL fragment above and regenerate the html
documents every time I want to switch style sheets, which is slow and
error-prone.  

So I was hoping there might be a better way to do this.

Thanks,
cga