A class for IronRuby users that will point the current AppDomain's configuration to a new configuration file.

configuration_settings_hackery.rb

require 'System.Configuration, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

class ConfigurationSettingsHackery
  def set_config_file(new_config_file)
    set_config_file_on_current_app_domain(new_config_file)
    refresh_current_client_config_paths
    reset_configuration_manager_to_force_reload
  end
  
  
  private
  
  def non_public_binding
    System::Reflection::BindingFlags.NonPublic
  end
  
  def non_public_static_binding
    non_public_binding | System::Reflection::BindingFlags.Static
  end
  
  def non_public_instance_binding
    non_public_binding | System::Reflection::BindingFlags.Instance
  end
  
  def set_config_file_on_current_app_domain(new_config_file)
    domainSetup = System::AppDomain.CurrentDomain.GetType().
      GetProperty("FusionStore", non_public_instance_binding).
      GetGetMethod(true).Invoke(System::AppDomain.CurrentDomain, nil)
    domainSetup.ConfigurationFile = new_config_file
  end
  
  def refresh_current_client_config_paths
    configSystem = System::Configuration::ConfigurationManager.
      to_clr_type.GetField("s_configSystem", non_public_static_binding).
      GetValue(nil)
    configHost = configSystem.GetType().
      GetField("_configHost", non_public_instance_binding).
      GetValue(configSystem)
    configHost.GetType().Assembly.
      GetType('System.Configuration.ClientConfigPaths').
      GetMethod("RefreshCurrent", non_public_static_binding).
      Invoke(nil, nil)
  end
  
  def reset_configuration_manager_to_force_reload
    initStateType = System::Configuration::ConfigurationManager.
      to_clr_type.GetNestedType("InitState", non_public_binding)
    state = initStateType.GetField("NotStarted").
      GetValue(initStateType)
    System::Configuration::ConfigurationManager.
      to_clr_type.GetField("s_initState", non_public_static_binding).
      SetValue(nil, state)  
  end
end

ConfigurationSettingsHackery.new.set_config_file('c:\\app.config')