Having separate plugins and themes folder for multi-site setup

Question

My multi-site setup uses sub-directory. I am creating one plugin + one theme to customize each of the sites. Is there any way to have separate plugins and themes folder per site like so or something similar:

root
+----wp-content
|     +----site1
|          +----plugins
|          +----themes
|     +----site2
|          +----plugins
|          +----themes
+----mu-plugins
|     +----shared-plugin1
|     +----shared-plugin2
+----plugins
|     +----optional-plugin1
|     +----optional-plugin2  

The goal is so that each site can only activate/deactivate the plugin/theme intended for it.

Edit

Multisite Plugin Manager can be a way to achieve what I want to do logically, though it does not put the plugins in their individual directories. I am still interested to hear other solutions.

Answer 1

There's register_theme_directory() to ... well register additional theme directories.

For plugins, we don't know how to get around it (so far). If you want, then you can jump into the discussion here and add your thought, share your try-outs and maybe we all together will come to an solution :)