Store value of exposed filter in var ($_SESSION or other)

Hello,

I want to store a value of an exposed filter in a variable.
In my view-view...tpl.php file I get my value with this code :

$view = views_get_current_view();
$viewArgs = $view->exposed_input['field_my_field'];

But I can't use this var outside of the my view-view...tpl.php template. I want to use this var in a node template.
I have tried to create this temporary variable in the template.php without success.

Have you any idea to create this var in my template.php ?

Thanks for your help.