2 multisites with different "files" folder each one

Hi, I'm trying to do a different 'files' folder on my two multisites.

I want this:

sites/my_domain1.com/ -------> themes
---------------------------------------> files <--- ***
---------------------------------------> modules
---------------------------------------> tmp

sites/my_domain2.com/ -------> themes
---------------------------------------> files <--- ***
---------------------------------------> modules
---------------------------------------> tmp

I was reading Setup of /sites directory for multi-site but it doesn't work on Drupal 4.7.x (or it doesn't work on my drupal 4.7.x webpage). .. On that page appears a special code for do this:

<?php
$conf = array(
  'file_directory_path' => str_replace(dirname($_SERVER ['DOCUMENT_ROOT']).'/','',dirname(__FILE__)).'/files'
);
?>

If I insert it on the settings.php of both multisites there appears the next error when I try to upload a file (image, audio..): "The selected file /tmp/tmp_CqsjhC could not be uploaded, because the destination image1.gif is not properly configured."... and the image is not on the sites/domain1.com/files/ directory :-(

Main doubt:

Does I need to write on "administer" > "site configuration" > "file system" the path: sites/domain1.com/files and sites/domain2.com/files (for my second multisite)?

---> If yes... all users will know I'm using multisites because they will see the full large path of the 'files' folder, and for this we don't need to insert this code on the settngs.php, do we?

---> If not... How should I solve this? Could someone explain me this, please?

Thanks for reading.