Use exec() if you can call it locally. If it needs to be invoked as a CGI (as in the script is designed to only work within a CGI environment), then you'll need to call it via include() or file_get_contents(). virtual() will flush your buffers and append the output of the sub-request.
You can pass parameters through include(), file_get_contents(), and virtual() as GET parameters:
If possible, go the exec() route. Using the other methods may require a config change.
When using exec(), you'll need to pass the arguments like you would for any CLI program.
foo val1 val2 foo param1=val1 param2=val2
How you pass the parameters in will depend on how you want to parse them out later in the other program/script. They'll show up in the called program like they would if you called it from the command line.