How can I use a variable inside a php file in a custom template?

[EquinoxWorld]

OK I just ran a VERY easy test. I made this file ... (Does not get ANY simpler)

PHP Code:

<?php

echo "hello world!!";


?>

Made this plugin:

PHP Code:

ob_start();
  require_once('test.php');
  $php_include = ob_get_contents();
ob_end_clean();
vB_Template::preRegister('COTW_SIDEMENU',array('php_include' => $php_include)); 


And added {vb:raw php_include} in my COTW_SIDEMENU template (which is being also rendered into all the other pages of my mod) but still nothing shows. I tried the same thing but in a regular template and it works fine so I'm guessing it has to be something to do with the fact that this template is being rendered into all the other templates, maybe an extra step is required??

I bet it's something real simple but I just can't figure it out.