You can't, or more accurately you do not want to (I'm sure it could be done, but it would be very unwise). File protocol is a filesystem access protocol. If you chain it to webservices for preprocessing, than you will not be able to open files properly. IE: I can open any file on my machine by typing in file://path/to/file.txt, so the last thing I want is to have it intercepted by webservers for preprocessing.
Always access it through the http protocol or on the command line via php.exe execution.
header('HTTP/1.1 420 Enhance Your Calm');