There's nothing in the Formidable Plus interface that allows for default values as you describe (though good suggestion). I think it could be accomplished with the Formidable filter `frm_setup_new_fields_vars`. It might look something like this:
add_filter('frm_setup_new_fields_vars','topquark_test',10,2);
function topquark_test($field_array,$field){
if ($field->id == '86'){ // Change to your field id
// Note, you'll need to update the value. The value needs to be an
// array of arrays. Each array within the larger array represents a
// row, and each value represents a column on that row.
// So, say your example had 1 row with 2 columns and the 1-5 scale appears in the
// second column. You would do this:
$field_array['value'] = array(array('','n/a'));
}
return $field_array;
}
You could put such a function into a plugin or the functions.php file of your theme.