[tbworld]

PHP Code:

// Three templates were created.  
//  1. block_custom - Custom block php/html template  
//      (Cloned from "block_html" template with added <vb raw variables> listed below).
//  2. my_template name - to be inserted in "block_custom"
//  3. ad_template - to be inserted in "block_custom"


// Outputs to "block_custom"  <vb: raw content>,  as inserted custom template
vB_Template::create('my template name');  
$templater->register('var1', $var1);   // Other template variables 
$templater->register('var2', $var2);   //    results outputted from PHP.
$output = $templater->render();  

// Output "ad_template" --- outputs to "block_custom"  <vb:raw ad_location>
$templater = vB_Template::create('ad_template');  
$templatevalues['ad_location'] = $templater->render();
vB_Template::preRegister('block_custom', $templatevalues); 


This is probably not exactly what you are looking for, but you can derive it from this.
This was modeled after the page @Lynne referred you to, it is revised for forum blocks.