Modify xsl:import value at runtime?

[Paul DuBois <paul@kitebird.com>]

I have a transform wrapper that begins like this:

<?xml version="1.0" encoding="utf-8"?>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"; version="1.0">

<xsl:import href="docbook-xsl/html/docbook.xsl"/>
...


So it imports the stylesheets from the docbook-xsl directory.
I would like to be able to select from among any of several
stylesheets: docbook-xsl-1.75.2, docbook-xsl-1.76.1, etc.
(For testing, or to enable different teams that all use the
same wrapper to select a different underlying DocBook XSL
stylesheet version.)

But I would like to be able to do the selectin at runtime rather than
by creating multiple wrappers that vary only in the xsl:import
line.

The href value cannot, as far as I can tell, be specified
using a parameter. Is there a way to accomplish what I want?
Perhaps using catalog entries?