It is possible to specify per-frame exit URLs for Swipable Gallery components in Google Web Developer. However, this functionality is not yet exposed through any Design View UI; you must edit the HTML in Code View to take advantage of this.
To demonstrate with an example: I've created a new document, added a Swipable Gallery component, and added three image frames to the gallery. After I switch into Code View, I see the component represented by the following HTML:
<gwd-swipegallery id="gwd-swipegallery_1" scaling="contain" class="gwd-swipegallery-e7iy" images="assets/search.png,assets/news.png,assets/mail.png"></gwd-swipegallery>I would like to link the first frame to
https://www.google.com/, the second frame to
https://news.google.com/, and the third frame to
https://mail.google.com/. I do this by adding a new "exit-urls" attribute to the tag. Its value must be a comma-separated list of exit URLs, like how the gallery's "images" are a comma-separated list of image URLs:
If there are certain frames which I don't want linked, I can just leave their entry in the comma-separated list empty. For example, if I didn't want the second frame to be linked:
Unfortunately, this is not currently supported by the other types of galleries.