[Samba] Macro Substitutions Printing . . .

[USTIC]

man smb.conf says:
The print command is simply a text string. It will be used verbatim after
macro substitutions have been made:

But then it says:
 With printing = cups, and if SAMBA is compiled against libcups, any
manually set print command will be ignored.

How can I use those macro substitutions to log printed pages ?
I used the following in the printer share:
root preexec = echo '%T:%U:%u:%G:%m:%M:%I:%J:%c:%z' >>
/var/log/samba/impresiones.log

but macros %J %c and %z are not substituted . . . .

Thanks for your help