If you have the IP addresses setup on your naked domain and your www cname'd to yourappname.herokuapp.com then all you need do is use something like RackRewrite in your application to redirect the requests when they arrive at your application.
What you want to setup is any request to the naked domain gets redirected to your www address. After following the installation instructions add an initializer in config/initializers
ApplicationName::Application.config.middleware.insert_before(Rack::Lock, Rack
r301 %r{.*}, 'http://www.yourdomain.com$&', :if => Proc.new {|rack_env
rack_env['SERVER_NAME'] != 'www.yourdomain.com'
}
end if Rails.env == 'production'
Which is saying, if the requested URL is not www.yourdomain.com then 301 redirect it to the www.yuordomain.com but only if it's running in production.
