How to allow custom flash keys in a redirect_to call in Rails 3

In Rails 3, you can pass has attributes directly to redirect_to to set the flash. For example:

redirect_to root_path, :notice => "Something was successful!"

However, this only works with the :alert and :notice keys; if you want to use custom keys, you have to use a more verbose version:

redirect_to root_path, :flash => { :error => "Something was successful!" }

Is there any way to make it so that custom keys (such as :error, above) can be passed to redirect_to without specifying it in :flash => {}?