Appropriate way to handle settings in Rails3 Plugin?

Question

I'm working on a plugin for Rails3. I'd like to allow users to override some settings. At the moment I'm doing this inside my plugin's Rails::Engine class like:

config.my_setting = :default_value unless config.respond_to? :my_setting

This seems like the wrong way to handle this. Is there a better method or convention most plugins use in Rails3?