EMBERJS : How to trigger an action in a child component?

I know the concept of Data Down / Actions Up, but I'm facing a situation on which I don't know how to do it with the DDAU. I searched on differents forum and blogs how to do it, but it does not fit my request.

I have a controller with two components. On the first component I have a header with a button. On the second component I have a form.

When the button is clicked, an action is trigered and catched by the controller, but how can I notify the second component of the "click" on the button on the first component.

An easy solution would have been to include the first component in the second one, but I can't do this because each component are used in many different situations.

Thanks for your help.