fileref-attribute with 'cgi'

Hi,
using DocBook-fo-stylesheets 1.72.0 and xalan; try to transform imagedata with unusual fileref-attribute:
<inlinemediaobject>
...
<imagedata format="gif" fileref="http://www.forkosh.dreamhost.com/mimetex.cgi?c=/sqrt{a^2+b^2}"/>
...
</inlinemediaobject>
Result in fo:
<fo:block space-before.optimum="1em" space-before.minimum="0.8em" space-before.maximum="1em" line-height="150%" margin="2px 0px 2px 2px"> </fo:block>

Don't get any error message, but 'inlinemediaobject' is ignored.
Is there a way to transform imagedata with 'cgi' in imagedata-fileref-attribute as described above?

thanks in advance
jürgen klein