What's the best wait for a plugin to autoload

Let's say I have a plugin for for ActionController. I only want the
plugin loaded if ActionController is loaded.

Rails has put a lot of effort into autoloading only the necessary
files during startup. Is there a good way for the ActionController
plugin to load only when the ActionController module is loaded?

For example, most plugins would do the following:

ActionController.class_eval do
  include UberControllerPlugin
end

The above lines cause all of ActionController to be loaded for all
tests and server startups. Is there a way to "autoload" the plugin
only after the ActionController module has been referenced?