%build  ALL=(nobody)  NOPASSWD: /full/path/to/script

##</code><code>##

# Are we the right user?
use User::pwent;
my $user_wanted = 'nobody';
my $user = getpwnam($user_wanted);

if ($< != $user->uid())
{
  exec(qw(sudo -u), $user_wanted, $0, @ARGV);
}
[...]