I did manage to do this using Hazel and a few simple rules that create alias' of the images in a dedicated folder which can be picked up by the screen saver.
Basically I have a folder structure like this;
Pictures>
- /+For Screen Saver
/Desktop Pictures
- /1. Nat Geo
/2. Aerial
/3. Cosmos
Hazel automatically searches the "Desktop Pictures" folder, finds any images, color labels them green, adds a spotlight comment "screensaver" and finally places an alias in the "+For Screen Saver" folder.
So any time I want to add a picture, I just drop it into the "Desktop Pictures" folder, or one of the classified subfolders and Hazel automatically does its magic.
Simples.
Here is the main rule.
https://dl.dropboxusercontent.com/u/224 ... hazelrules
The second rule cleans up any duplicate alias' created, based on the Finder copy naming convention of adding -1 to the end of a file name.
https://dl.dropboxusercontent.com/u/224 ... hazelrules
Enjoy.