Generate KML file at Registration

I wasn’t sure if this should go under hacks or multi-site. My apologies if it’s in the wrong forum

I’m trying to figure out how to get the submit button in the registration form to generate a new unique KML file for each user that registers with the site. At this point I am not worried about what is in the KML form. That I can figure out.

Google has this tutorial for creating a KML file using PHP, but I don’t know how to call the PHP file that generates the KML file from the submit button, and not interfere with the regular registration procedure.

So, using that tutorial’s phpsql_genkml.php the site would generate a PHP file that has the User’s ID in the filename, ie: user456.kml.

Any help would be much appreciated.