To the best of my knowledge- Previews must be in the same folder system as the catalog. So the answer is -no!
Why would you not consider moving the catalog to another hard-drive or folder location?
(and Smart Previews may only be needed if your master image files are in a location that can be dis-connected)
You cannot practically separate the catalog from the previews.
However the catalog and previews can reside almost anywhere so you could shift them all.
Personally I keep my catalog and previews on a dedicated fast external drive as disk access is not constrained then.
As the Previews and Smart Previews are in their own sub-folders, can't you just exclude those subfolders from your backup routine? I do that with my backups.