What Am I Doing Wrong?

Explanation

The below doesn't work. Even if Observed.observer_instances shows and instance of Observer when you save an Observed instance nothing is hit inside the observer. 

If you register the observer in application bootup as per normal and specify "observe Observed" inside the Observer then of course it works. 

What magic do I need to weave to allow a class to register itself with an observer rather than the observer register itself with the observed classes? 

observed.rb

class Observed < ActiveRecord::Base
  # include Auditing - would be repsonsible for providing
  # def auditing( mode )
  #   Observer.register_class( self, mode )
  # end
  Observer.register_klass( self, :mode_for_later ) # Would like to mixing a class method auditing( mode ) so self is implied
end

observer.rb

class Observer < ActiveRecord::Observer
  @mutex, @class_map = Mutex.new, {}
  
  def self.register_class( klass, mode )
    @mutex.synchronize do
      klass.add_observer( self.instance )
      @class_map[ klass ] = mode # I plan to use this later
    end
  end
  
  def after_save
  end
  
  def update( *args )
  end
end