thanks all. the solution we used was a combination of
reorganization and the resource-exists action
<map:match pattern="*/*/*"> <!--
domain/page/action -->
<map:act
type="resource-exists">
<map:parameter name="url"
value="c:/mag/xsl/{1}/{2}.xmap"/>
<!-- mount domain-specific sitemap
-->
<map:mount
check-reload="yes" src=""
uri-prefix="{1}/{2}"/>
</map:act>
<!-- otherwise mount
default sitemap -->
<map:mount
check-reload="yes" src=""
uri-prefix=""/>
</map:match>
