You can create an async Insert Business Rule on the sc_req_item table.  If you want the attachment(s) to appear in the header instead of the activity stream, use this script.

(function executeRule(current, previous /*null when async*/) {
	var attach = new GlideRecord('sys_attachment');
	attach.addQuery('table_name', 'ZZ_YY' + current.getTableName());
	attach.addQuery('table_sys_id', current.sys_id);
	attach.query();
	while(attach.next()){
		attach.table_name = current.getTableName();
		attach.update();
	}
})(current, previous);