// put this in your template.php's hook_preprocess_user_profile(&$variables)

// admins can masquerade as specific users
if (isset($_SESSION['masquerading'])) {
  $block = masquerade_block_1();
  $variables['masquerade'] = drupal_render($block);
}
elseif (isset($variables['elements']['masquerade']['#markup'])) {
  $variables['masquerade'] = $variables['elements']['masquerade']['#markup'];
}

// put this in your user profile template
<?php if (isset($masquerade) && $masquerade): ?>
  <?php print $masquerade; /* lets admins simulate what it's like to be a specific user */ ?>
<?php endif; ?>