plugin.rb

# lib/account_with_account_domains.rb:
Account.class_eval do
 # ...
end

# init.rb:
configure_method = Proc.new do
  ::ApplicationController.promote_view_path File.dirname(__FILE__)+'/app/views'
  require_dependency 'account_with_account_domains'
end

if CANVAS_RAILS2
  Rails.configuration.to_prepare(&configure_method)
else
  class MyPluginRailtie < Rails::Railtie; end
  MyPluginRailtie.config.to_prepare(&configure_method)
end