In this case I think you would need to code your own AJAX query. The JavaScript involved for the post object field is not loaded on the field group editor page. In my experience you can use any type of a field for a field setting as long as it does not require JS, fields that requires ACFs JS generally fail to work as expected. An example is adding a default image setting to an image field. To do this you need to load the WP uploaded on the field group edit page manually.
