This was published in SysAdmin Mag a while back it'll automount the share on demand. I used it for my iTunes library when it used to be on a samba share. It kinda assumes you know what you're doing in the terminal tho:
1 - Make sure fstab is in sync with the current NetInfo settings by running:
nidump fstab . >> /etc/fstab
2 - Edit fstab to include a line similar to the following
server:/share /Network/Servers url url==smb://user😛assword@server/share,net 0 0
(that should say user : password above, i couldn't get it to turn the smilies off)
Replace 'server', 'share', 'user' and 'password' with the required settings
3 - Load new fstab into NetInfo
niload fstab . < /etc/fstab
4 - Reboot and find the volume available under /Network/Servers/server/share
5 - Repoint iTunes if necessary and you're done.