On unix I its as easy as copying the PHP.ini and creating a small shell script and setting it up to use them from Apache. I do it on my unix system as I have three virtual hosts - each of which uses it own PHP.ini .
Shell Script:
#!/bin/sh
/usr/local/lib/php -c /path/to/php.ini $1
You'll need to change change the path accordingly in your Apache configuration. For example if you shell script is kept in your CGI-BIN and called php you would use the following:
php cgi config
AddType application/x-httpd-php .php
Action application/x-httpd-php "/cgi-bin/php"
I'm not sure whether this carries any security concerns. As long as that shell script is outside the document root and has only read and execute permissions it should be fine.
