Document Root of a Virtual Directory

Hello,

is there any possibility to serve a script (in this case PHP) with the absolute path of a virtual directory?

ex.: "http://127.0.01/~Dormi" is mapped to "/users/Dormi/web" while "http://127.0.01/" is "/var/www". is there any way to pass the virtual directory's path (maybe .htaccess?) to the script?

thanks in advance