In the next version of Piklist you will be able to do this with the piklist_get_file_data filter:
EXAMPLE:
Allow Piklist to read “User ID” in comment block
add_filter('piklist_get_file_data', 'allow_user_id', 10, 2);
function allow_user_id($data, $type)
{
// If not a User section than bail
if($type != 'users')
{
return $data;
}
// Allow the comment block to read the "User ID" attribute.
$data['user_id'] = 'User ID';
return $data;
}