There maybe some confusion. Both cbr and car files can be saved w/ thumbs, Just save a car file ,which is a scene file as a preset. Perfect for a sky.
Easiest place is to save them as a car file, w/ comments and a preview under the my presets directory under my documentss/daz /carrara. (on windows) Then just go to your scene tab if you need to to make sure that folder is added to the browser. Think it is by default, but not sure if there is a my scenes folder. I think I made this to go under that my docs, then added it to the browser so I can put scene presets there. It's not hard just a bit manual.

Previews have to be saved w/ that option checked for the file.

Keep in mind that the C browser is particular about what file goes on what tab. The misc tab is a bit more flexible. But you can add a folder or update the info. If a folder is added and you see it listed in the treeside, but nothing is showing on the view side of the browser you have the file in the wrong category.

No need to think outside the box....
    Just make it invisible.