How to get other variables than the $form in theme_name_form function ?

I was wondering if anybody can help to get other parameters to the theme_name_form function ?

Example : I fill the form variable with the item I want. I call the theme_name_form which render the form correctly.

How can I have another variable which come from name_form into my theme_name_form() ??

This is what I tried :
in the .module file (hook_theme) :

    'macommande_formulaire' => array(
	'arguments' => array('commandes' => array(), 'total_commandes' => null ),
	'file' => 'macommande.page.php')

and in macommande.Page.php

function theme_macommande_formulaire($form) {
	if ($total_commandes) output.= "Yess :-) ";

And I can't access to the value of $total_commandes... :-(

I assume the second function doesn't know at all about my variable $total_commandes... but how can I pass this value (without a static variable of course ;-) )

Thanks !