Hello. If it's OK for you to write some custom code and make some changes in DB:

INSERT INTO `sys_objects_privacy` (`object`, `module`, `action`, `title`, `default_group`, `table`, `table_field_id`, `table_field_author`, `override_class_name`, `override_class_file`) VALUES ('bx_polls_allow_view_to', 'bx_polls', 'view', '_bx_polls_form_entry_input_allow_view_to', '3', 'bx_polls_entries', 'id', 'author', '', '');

It's privacy object for "Visible to" field in polls. You may use custom class/file here `override_class_name`, `override_class_file`. For now, you may even put the class in the polls/classes/ folder and it won't be overwritten untill UNA decides to do the same in core.

Then you need to overwrite 'addSpaces' method in your class.

public function addSpaces($aValues, $iOwnerId, $aParams)

It's used to add contexts in the list. Something similar you may find in Timeline BxTimelinePrivacy class.

Good luck!