Turn off tinymce based on input format

I'm trying to use wikitools wtih my book content type. I've created an input type called wiki. However, I want to unload tinymce when the selected format type is wiki. Using the tinymce module I could do this:

function phptemplate_tinymce_theme($init, $textarea_name, $theme_name, $is_running) {
//disable tinyMCE in case the input format is wiki or Flash
 if (is_numeric(arg(1)) && arg(2) == 'edit') {
    $node = node_load(arg(1));
    if ($node->format == 5 || $node->format == 4) {
      unset($init);
    }
  }
  // Always return $init
  return $init;
}

With the tinytinymce module I don't know which function to call so as to unset $init.

Thanks for your help.