I would go with adding an empty `{% block additional %}{% endblock %}` here. That way you don't have the template go running around looking for `all include` unnecessarily.. 

To use it, simply drop override it with your own version of `_admin_edit_blocks.tpl` and then use [overrules](http://zotonic.com/docs/latest/ref/tags/tag_overrules.html#tag-overrules) to inject your code into the "additional" block.