I may have found a paid solution: http://myproofs.co/index.php/my-proofs-plugin/
Specifically for photographers, this is exactly what I was thinking about. I can't tell if it only works with zenfolio, or if there's a way to send to any URL with a code. I'm going to download it and take a look. I also can't tell if their pricing section applies to this Wordpress plugin....hmmm...