This is more or less conjecture, but you could possibly put an AddType directive in .htaccess or apache conf like...
AddType application/x-httpd-php3 .
... but I honestly don't know if that would work.
One way around maybe to create a directory with the name you want and place a index.php inside that directory, and that would give you a similar result.
Overall, why do you want this behaviour? Maybe knowing the application could get you some different methods or ideas.