Yes it's possible, I do this with my header and footer and then just have one liners in the two templates. First of all you need to create a plugin. The parse_templates hook works well for me.
PHP Code:
$templater = vB_Template::create('custom_template');
$templates = $templater->render();
vB_Template::preRegister('footer', array('custom_template' => $templates));
And then inside the footer template (in the example above as that's where I registered the custom template) you just do:
Code:
{vb:raw custom_template}
Basically you need to register your custom template as a variable which you can then use in the template you just registered it for.