Approval Workflow on instance level

approval_workflow.rb

def approval_by(role)
  singleton_class_with_workflow = class << self
    approval = self.class.approval_transitions_for[role]
    workflow do
      (approval || []).each do |state_name, events|
        state state_name do
          events.each do |event_name|
            event event_name, transitions_to: EVENT_RESULTS[event_name]
          end
        end
      end
    end
    self
  end

  singleton_class_with_workflow.workflow_spec
end
approval_by(:administrator)
#NoMethodError: undefined method `approval_transitions_for' for Class:Class

Essentially self.class is not the "regular" class but the the class of the singleton class. I need a class-level attribute inside the singleton class.