Sandboxing and creating folders

When a user drags a file into your sandboxed app, it automatically has permission to ‘use’ that file.
But is there a way to create a new file or create subfolder in the folder where that file exists?

For example:
Lets say the user drags a file from his desktop into your app and you now want to create a folder onto the desktop.
Using .createfolder does not work because you do not have permission to do so (sandboxed remember).

Is there a way to do this?