Combining validation error messages

I used Ryan B.’ Railscasts episodes 73-75 to build forms with
dynamic added models in complex forms. Everything works great, but
displaying validation errors are a big mess since it displays it’s own
box for each individual error, including an error for each invalid
child record in the parent box.

How can I group the errors to display in one box for all the
dynamically added models and the main model?
I found this solution, but it doesn’t really work for dynamically
added models and looks super ugly if you try to use it with Ryan B.
style forms:

<%= error_messages_for :every, :single, :model %>