Make uploads live outside of the WP folder

Question

I'm working on a template that basically sets up WP in the following manner:

• /
• /wp
• /content/plugins
• /content/themes
• /media

Using the /media folder to store and serve uploads on single-site installs is easy enough:

add_filter('pre_option_upload_path',      function($val) { return '../media'; });
add_filter('pre_option_upload_url_path',  function($val) { return '/media'; });

It seems a bit less trivial to change for multi-site installs. A cursory look in the WP code yields functions like ms_upload_constants() and all sorts of checks related to is_multisite() whenever uploads occur, and cursory googling yields little to nothing.

Is there a documented procedure to make a WP multisite do a similar trick with /media/$site_id in the above setup? Or is it primarily a matter of tricking WP into writing into the correct location by using symb links (or something to that order)?