How do I call extern.php and pass arguments without extrnal reference?

I can, (but have been advised against for perfomance reasons) call extern.php via an external reference and pass parameters to it thorugh the URL.

include('http://www.mysite.com/punbb/extern.php?action=active&show=5')

So how do I call it from the local file system AND pass parameters to it?
Do I have to copy the script and hard code the parameters in?

--Alan