If you want to do this from a DA, does that mean you don't want to refresh the page?
If the page won't be refreshed and you want to make the message display you could do this technique taken from Dan McGhan's Modal plugin.
.append("Your Success Message Here")
This approach is dependent on the Theme you're using. Here your inline notification is inside an ID of #messages, you may need to change this.
The code finds your messages div/section/element, then hides it, in case there's an old one. Then the new message is added and displayed with slideDown.
You may also want to add more to your message to style it in the same fashion as your themes message.
For example: <div class="success">Your message here</div>
Let me know if this doesn't get you close.
you can try using http://deneskubicek.blogspot.com/2013/06/create-success-message-using-dynamic.html OR http://deneskubicek.blogspot.com/2013/05/create-success-message-using-dynamic.html from Denes' blog.