Possible to exclude specified accounts from backup?

I searched, but couldn't find a good answer to this simple question.

How can we exclude specific accounts from the backup process?

I thought there would be a system like the stats system, where we can just "click click click" to select/unselect accounts to include in the backup process... but I can't find it.

Am I blind, or is this feature missing? It's all or nothing for backups?

Thanks!