DOCBOOK-APPS: Setting OpenJade output filename?

Maybe I don't understand the documentation for OpenJade's -o qualifier,
but I can't set OpenJade's output filename.

The shell command (on Linux Red Hat 7.1)

  openjade -t sgml -d ../aspectjdoc.dsl#html -o progguide.htm progguide.sgml

produces many files called *.htm, but none called progguide.htm. I
worked around this behaviour with

       (define %root-filename% "foo")

in my customization layer, but I'd rather do it on the command line.
That way I can share the customization layer for multiple documents.

Is there a way? 

Thanks.

-- Vladimir