具有隔离范围的嵌套指令中的双向绑定延迟

I have a controller containing a directive with an isolated scope. Whenever a user changes the value in the directive's dropdown, I need to notify the controller about the change. I do this by providing the directive with a callback function, and calling this function on ng-change event in the directive's dropdown. I can't (and don't want to) use watches in the parent controller, as I'm only interested in user-generated changes here. I have a controller containing a directive with