Add book parent when translating a book page

If I translate a book page the parent is not set automatically although the parent page is already translated. If I add &parent=n The parent is set.
So, when I can do it manually, it should be possiible to do it automatically according to the following rules:

1. Is the current node I want to translate a book page?
2. Is sync module activated and this node type set to sync with book parent?
3. Is the book parent of the current node translated into the desired language?
4. add "&parent=bid" to the url, where bid is the book ID of the translated parent node

If I was a php programmer, I would do this myself!