[Samba] passwd program example for parsing new password typed?

[Gianluca Cecchi]

hello,
I have two domains, one w2k3 and one with samba 3.
The users log on to the samba domain and use outlook connected on
exchange on w2k3 domain.
pwd age for the two domains is aligned.
On another samba 3.0.23c linux machine inside the w2k3 domain (ads
security  parameter set) I have set up a script that allows to change
the w2k3 domain password for the user, using ldapmodify command to
change the "unicodePwd" parameter of AD.
This could allow me to synchronize the passwords of the two domains'
users during the normal windows password change operation.
I have only to set up the "passwd program" of smb.conf accordingly.
By default it is "passwd %u" and I read that it makes use of expect to
get the passwd typed by the user.... (not clear how... where to find
docs?)
I would like instead to substitute it with a script that
1) runs the passwd program locally as by default
2) runs a remote shell to the other samba host to run the script
specified above for AD change.
Any hint on how to give to the script the password typed by the user?
Thaks in advance for your help.

Gianluca