Shoot. I should have thought about that doubling. Instead of using the URL for the featured image, use the URL to one of the images in the gallery and then remove the image from the gallery. That should still cause the image to be visible in the gallery, but only once.
It’s also possible to link to another gallery. Just match the ID of the gallery you’d like to link to and the link will open it instead of the one in the home block where the link is. You could create a series of links that actually open all of them from one home block if you wanted to.