Adding data before save in CakePHP

Post hasMany Tag:
My form:

$form->input(''); //1st tag
$form->input(''); //2nd tag

This works perfectly, but...

I create some fields, and I want add each time one tag by $this->data['Tag'][some_number]['name'] = 'all';
Do not ask me why i want that, but tell me how i can add 'all' tag in my model to each Post?

This should get effect 4 INSERT sqls: one add post, and three: 1st tag, 2nd tag, all tag.

More explain: How add more tags without form fields? How add default tags? No input hidden, only pro solutions:)