Daniel,
Prompted by this question, I've updated the fopub script to pass parameters directly through to fop. One of those parameters you can set is the orientation.
Here's the command you can use to set the orientation:
./fopub README.xml -param page.orientation landscape
All arguments after the source file name (in this case, README.xml) are now passed to fop.
As an alternative, you can set the parameter directly in the fo-pdf.xsl template:
<xsl:param name="page.orientation">landscape</xsl:param>
You can also use this feature to set any parameter defined in DocBook XSL [1]
Cheers,
-Dan
p.s. Note that this feature is only available in the Unix version of the script atm.
[1]
http://docbook.sourceforge.net/release/xsl/1.78.1/doc/param.html