[MarkFL]

Okay, here's my workaround:

The "mytemplate" template:

<div>
	<vb:if condition="$notifications_total">
		there are notifications
	<vb:else />
		no notifications here
	</vb:if>
</div>

The plugin, hooked at "process_templates_complete":

PHP Code:

$templater = vB_Template::create('mytemplate');
    $templater->register('notifications_menubits', $notifications_menubits);
    $templater->register('notifications_total', $notifications_total);
$ubermenu = $templater->render();

$header = str_replace('{ubermenu}', $ubermenu, $header); 


Now, in your "header" template, put the string "{ubermenu}" wherever you want the rendering of "mytemplate" to appear.