Rails middleware initialization block
Based on tapajos comment, I was able to to refactor the code using initializers. First I created one to load the configuration file:

APP_CONFIG = YAML.load_file(File.expand_path('../../config.yml', __FILE__))


Then I created another initializer, like this:

superfeedr_config =  {
      :host     =&gt; APP_CONFIG["general"]["hostname"],
      :login    =&gt; APP_CONFIG["superfeedr"]["username"],
      :password =&gt; APP_CONFIG["superfeedr"]["password"]
}

Rails.configuration.middleware.use Rack::Superfeedr, superfeedr_config do |superfeedr|
    Superfeedr = superfeedr
    superfeedr.on_notification {|notification| Article.create_from_raw_notification(notification)}
end


I also applied the logic described in this SO question to ensure the load order: How do I change the load order of initializers in Rails 3?.