To give an example of how I tried to implement this:
I created a folder "PrivateFolder" off the root of the site
I created a user "Me"
I created a role "FolderUser", and assigned "Me" to it
In the permissions of "PrivateFolder" I set an explicit "grant view" to "Me"
In Pages, Permissions for all Pages, I set an explicit deny to "FolderUser"
As I understand, the explicit deny to FolderUser at the all pages level will not allow Me to see files, except for the folder PrivateFolder and its children, where the explicit grant will win, and so I can see Private Folder and its files.
In practice, when I am logged on as Me and click Pages, Sitefinity says "Loading" and never returns any pages list.