Hmm...this is an interesting one. Since you don't know the names of the subfolders it's going to be almost impossible to script. How many users are we talking about? What you can do is use the full client, unlock all your archiving settings and as long as you have permissions to your users archive, create an outlook profile to that user and manually modify the archiving settings sa needed per folder.
The only thing I'm unsure of is since your parent folder will be set to do not archive, I'm not sure if ev will continue to process the sub folders under them.