Builder::XmlMarkup and dashes

Has anyone hacked Builder::XmlMarkup to dasherize underscore tags by
default? I know I can use tag!, but I'd like to find a way for it to
translate underscores to dashes automatically. In other words:

xml.department_manager do
  "fred
end

#=> <department-manager>fred</department-manager>

I tried hacking Builder::XmlBase.method_missing but got myself all
twisted up!

Thanks.

Steve

xml.tag! 'department-manger', 'fred'

Right, I know about 'tag!' but I was hoping to rig things such that
XmlMarkup always called 'dasherize' on element names.

Steve