Make the "Add to Favorites" link inactive after it's been clicked?

Hi all,

Currently, DirectoryPress displays the “Add to Favorites” link on all listings, even if the listing has already been added to the visitor’s favorites.

I’d love to find a way to make the Add to Favorites link dimmed, inactive, or gone entirely if a particular listing has already been added to a visitor’s favorites. But I’m running into trouble trying to find a way to do that.

There doesn’t seem to be a built-in way to do this. Fine, I’m willing to wade into the code. But I don’t want to break anything or hinder the performance of my site.

I see at PPT/ajax/actions.php, there’s a section called Wishlist that seems to be relevant. I’m guessing that copying that SQL query onto the _item.php or _single.php templates is probably a bad idea from a server performance perspective.

What’s the best way to make this happen?