integrating "Corresponding node reference" and "nodereference_url"

Hi all!
I'm trying to build a book-like content tree based on node references.

I woluld like automatically creating these relationships:

Parent --- a --> Child
Parent <---b --- Child

by means of two modules which automatically set node references:

http://drupal.org/project/nodereference_url
http://drupal.org/project/cnr

1. nodereference_url puts an "add Child" link on Parent page, letting you create a new Child and setting Child's nodereference to its parent automatically. (noderef "b")
2. Corresponding node reference updates Parent nodereference toward a Child (noderef "a") when Child's nodereference toward its Parent is set. (noderef "b" at point 1)

However CNR works only when both Parent and Child node references have unlimited values set.
With nodereference_url there is no choice at all.

It would be great if these two modules would work together...any help/idea?

Thank you in advance,
Andrea.