Link Gallery Thumbnails to Image's Link URL

I’m using the Twenty Ten theme and I’ve inserted a gallery of 4 images into a page.

Each of the images in the gallery has a custom Link URL set, however with Twenty Ten’s default gallery setting, I can only have it link to the image file or the attachment page.

How can I change the thumbnails to pull from the Link URL that’s set on each image when clicking on the gallery thumbnails?

Thanks!

-foo