Mount smb share as local directory
You need to understand how mounting works. In short what you want is to:


Mount your smb:// drive on a certain location.
Use your file:// command as you always do.


When you use 'Connect to Server' - ⌘K, your drive should be mounted somewhere in /Volumes/. So now you can use file://Volumes/drive-name.

For normal use, like this, a mounted network filesystems can be treated just like a 'local' file system. There is no difference in use.

How to mount network drives automatically is another story and can be found on SO, for example https://superuser.com/a/367730/246895