The following function returns the hierarchy of the first-found instance of a key an array. The concept was to take a renderable array, and build the $parents array as required by drupal_array_get_nested_value.

drupal_array_get_nested_key_parents.php

<?php
/**
 * Returns the hierarchy of the first found instance of a key in an array.
 */
function drupal_array_get_nested_key_parents($needle, $haystack, &$parents = array()) {
  foreach ($haystack as $key => $value) {
    if ((string) $key == (string) $needle) {
      $parents[] = $key;
      return TRUE;
    }
    elseif (is_array($value)) {
      $tempKey = $parents;
      $tempKey[] = $key;
      if (drupal_array_get_nested_key_parents($needle, $value, $tempKey)) {
        $parents = $tempKey;
        break;
      }
    }
  }
  return FALSE;
}