Creating a dedicated directory for "other files" for each site in multi-site

I have a client who has a multi-site network running in the sub-domain configuration. They want to utilize a directory for each site to store “other files” relative to each site.

I have tried creating a directory under each site in its appropriate folder in the blogs.dir directory but get a 404 error when I try to navigate to it.

How do I make this directory visible and prevent the WordPress install from using it?

I have done this numerous times in a stand-alone install of WP with no problems and have even installed another version of WP in this sub-directory which is what this client would eventually like to do in this case. But for now, I am just trying to figure out how to make this directory local to each site and be recognized.

Thanks in advance for any insight on this.

[moved to Multisite forum]