Rails 3.1 PDF Render

I'm trying to figure out how to convert a Rails plugin I wrote that
handles a custom PDF render that works in Rails 2.3.9 but doesn't in
Rails 3.1. What we have is a separate server that actually does the
PDF generation of the webpage and then sends this back to the Rails
app. The plugin is located at https://github.com/amkirwan/too_rendermonkey.
I understand in Rails 3 alias_method_chain is gone and I should use
ActionController::Renderers.add. I've looked at the example at but I
can't seem to get it to work http://www.engineyard.com/blog/2010/render-options-in-rails-3/.
If I do something like the following:

module TooRendermonkey
  def self.run
    ActionController::Renderers.add :pdf do |pdf, options|
      _render_option_pdf(options)
    end
  end

def _render_option_pdf(options)
    ....
end

end

I can see from the console that the :pdf is registered but it never
gets called from the Rails app as far as I can tell.

ActionController::Renderers.class_eval do
   self.const_get(:RENDERERS)[:pdf].call
end

Any help would be appreciated.