When I was working on a similar issue for django-selectable I created an issue to address this problem with a simple proof of concept patch
https://code.djangoproject.com/ticket/15760. However I never followed through with the ticket to try to get something like this added. In the meantime another ticket was created and fixed which solves a large portion of the problem
https://code.djangoproject.com/ticket/18241. With this change you can catch the click event of the add button. I still feel like the admin inline javascript is not particularly flexible and having some clearly documented hooks for this use case would be nice.