Modularity: how to "parametrize" the href attribute of

I have to maintain a local XSL stylesheet for DocBook. It defines
local rules and imports Norman Walsh's classic stylesheet for most of
the work. So I write:

<xsl:stylesheet>

<xsl:import
  href="/usr/share/sgml/docbook/stylesheet/xsl/nwalsh/html/docbook.xsl"/>
<!-- The default value is for Debian. -->

... Local rules goes here

</xsl:stylesheet>

The problem is that our local stylesheet is used on a network of many
different Unix machines, each installing Norman Walsh's stylesheet in
a different place.

Using <xsl:param> does not seem to work: <xsl:import> must be the
first element so I cannot define a parameter first.

The only solution I see is catalogs. Besides added complexity and yet
another XML beast to learn, it would force us to have a properly
managed catalog on each machine.

Is there a better way?

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list