Multiple "html.stylesheet" declarations for one document

[Bernd Pörner <bernd.poerner@imformgroup.com>]

Are there any possibilities to use multiple

<xsl:param name="html.stylesheet" select="'xxx.css'"/>

declarations in my customization layer?

My problem is that I have to reference up to five css stylesheets and 
when I use more than one I get a "Duplicate global variable declaration".

B.