You can do this using field keys, however, it still will not work the way you expect it to work without including the entire repeater. The reason is that ACF will not know when this field is submitted that you want to add a row to a repeater.
To accomplish what you intend you will need to create a new field group that has the fields you want on the front end form. Then you will need to create an acf/save_post action that gets the values of these fields and adds a row to the repeater field.
