[Samba] Samba users without local unix users

[Felipe S. Elich]

Hello to all:

First of all, sorry about my poor english. I am spanish :)
I have a debian machine running as a samba file server. The important part
of smb.conf is here:

   security = share
   encrypt passwords = true
   passdb backend = smbpasswd:/etc/samba/smbpasswd
   obey pam restrictions = yes
   invalid users = root
   passwd program = /usr/bin/passwd %u
   passwd chat = Enter\snew\sUNIX\spassword: %n\n
Retype\snew\sUNIX\spassword: %
n\n .

I want to create samba users without local unix account. I've tried the
following:

smbpasswd -a newuser

This command fails if newuser doesn't exist in local machine
(in /etc/passwd). If the user exist, the smbpasswd -a command runs well.

How can i create samba users without create local unix users?

Thanks in advance