Is there a way to prevent uploading assets into a parent level folder? Say that I have a folder structure like this:

/images
  /products
  /employee-photos
  /user-photos
  /advertising


Is there a way that I could define the single asset source of /images while only allowing uploads to its children?

I would like to do this so that I could simply add new children w/o having to define them as assets sources separately.
The only way I know how to do this would be to create a different asset channel for each child directory.