Not really. In the way such pre-packaged things usually are, TVs do have some limitations due to the fact that what was coded is what you get.
case 'DIRECTORY' :
$files = array ();
$path = $modx->config['base_path'] . $param;
if (substr($path, -1, 1) != '/') {
$path .= '/';
}
if (!is_dir($path)) {
die($path);
break;
}
$dir = dir($path);
while (($file = $dir->read()) !== false) {
if (substr($file, 0, 1) != '.') {
$files[] = "{$file}=={$param}{$file}";
}
}
asort($files);
$output = implode('||', $files);
break;
If you were willing to hack the manager/includes/tmplvars.commands.inc.php, you could add a line
$output = implode('||', $files);
$output = '||' . $output;
break;
Even better, if you are good with javascript and the DOM, you could create a custom rule for ManagerManager to add the empty option to the beginning of the select via javascript.