Hi there. I also needed this for a good client of mine and couldn't find it anywhere. He wanted to use it sort of as a user friendly way for clients to "proof" pictures. So the idea is that you create a gallery, then put it on a page, then password protect that page and send the client a link and password...and then they can favorite the images/photos they like or want prints of.
Here it is:
Let me know if you'd be interested in getting this mod or adding any features to it. We could give you the source files and install it for you for $25. I had to pay the coder, so I'm still a little in the negative...otherwise, I'd charge way less! If you know of others that need it I'll drop the price to $10 if we find 5 buyers!