I suppose, an alternative to keep the 'api' but remove the method missing would be to define configurable settings via a macro that generates instance methods.  Then you can also ensure only valid keys are set. e.g.

```ruby
@configurable_settings = []
class << self
  attr_reader :configurable_settings
  def setting(*settings)
      Array(*settings).each do |setting|
         add_setting(setting.intern)
      end
  end
  def add_setting(setting)
  end
  private :add_setting
end
setting :foo, :bar
setting :baz
```