How to make a region available to a non-page tpl file?
Sure, you can use a node_preprocess() hook to create the variable much like this:

function mytheme_preprocess_node(&amp;$variables) {

   // whatever else you are doing goes here


   $block = module_invoke('AddThis', 'block', 'view', 0);
   $variables['mynewblock']=$block['content'];

}


which would call the AddThis module to invoke it's block hook and return block with delta 0.  

Lots more detail can be found here:  http://www.pixelclever.com/how-insert-a-block-a-tpl-or-content-programmatically-with-drupal