Tricky setup an images folder vs IIS

Hi,

I have an interesting and challenging design question.

I have a web application under iis and server is under VPN.

This web application works fine and lately i added a module which reads HTML files in another drive (not under iis).

Now, a customer needs to upload some html files which refers relative path for images in that folder with those htmls

And this fails as images folder is not under iis and i don't want to put those files together with this web application.

Now, what should i do? How can they upload those files?
1) Is it possible not to give access for ftp? This customer should have limited access.
2) Setting up a network share in which the images are in a shared folder? The network share idea fails as the machine is not in the same domain.
3) Uploading files to another images folder in IIS via button in interface? No, we don't want that.
4) Uploading via ftp? We don't want to open a port for that customer.

Am i missing any scenario? Our aim is to give minimum access to server itself. Any brilliant scenario option?

Br.