IZWebFileManager use MapPath api to resolve physical path. It is from security reason, to prevent access to file system outside application root.
But you still may have access to folder out of physical root, if it is mapped as virtual directory in IIS.
let say you have two folders:
C:\Inetpub\wwwroot - web app. root (~/)
C:\files - files to browse with file manager
You may map "files" as virtual directory into you web app. and get access to it from web app. (~/files)
In additional you may set up permissions for this directory to not allow script execution and browsing,
There is now to create virtual directory:
http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/b20a24a9-c472-44cc-a75b-ffe02989012b.mspx?mfr=true