Apache: use both PHP module and PHP-CGI

I had a need the other day to configure apache so it uses the PHP Apache module for all directories except one, where I wanted it to use the cgi version of PHP. The apache module is more efficient, but runs as part of the apache process. I wanted one URL to run in its own process. (I was troubleshooting and had a hunch this might help; luckily it did in this case!) Instructions for both Linux and Windows follow.

On Ubuntu I needed some preparation: 1. install the php5-cgi package (different from php5-cli, which is what we use when using php from the commandline); 2. enable the actions module.
On Windows I was using xampp, which follows an Everything-But-The-Kitchen-Sink philosophy, and all I needed was already there.

Here is the code I added (to my VirtualHost). First for Ubuntu:

ScriptAlias /usephpcgi /usr/bin
Action  application/x-httpd-php-cgi  /usephpcgi/php5-cgi

And then for Windows XAMPP:

ScriptAlias /usephpcgi C:/xampp/php/
Action  application/x-httpd-php-cgi  /usephpcgi/php-cgi.exe

(That is copy and paste from working configurations, so I think the trailing slash must be optional!)

Then for both Apache and Windows:

AddType application/x-httpd-php-cgi .phpcgi

Now, I have to admit my dirty secret: I cheated. Instead of enabling php-cgi for all *.php in one directory, I left *.php going to the Apache PHP module, and I created the *.phpcgi extension to use the cgi binary. Initially this was simply because I managed to get it working that way; but on reflection I realized I preferred it: I can switch a script between using php module and php-cgi just by changing the extension; also I can use php-cgi anywhere in my VirtualHost. If that does not sound so useful I should explain the script in question is already hidden between an Alias, something like this, so no public-facing URLs need to change:

AliasMatch ^/admin/(.*?)/(.*)$ /path/to/admin.phpcgi

What about my original plan to configure it for a directory, without changing the file extensions? I had trouble with this, and gave up on this; but Ben kindly left a comment, so now I know how to do it. First, you still need the ScriptAlias and Action directives shown above. Then it is simply this.

<Directory /var/www/path/to>
    <FilesMatch "\.ph(p3?|tml)$">
        SetHandler application/x-httpd-php-cgi
    </FilesMatch>
</Directory>

As Ben explains (see comment#1 below) the reason we need the FilesMatch inside the Directory is because mod-php is setting a global FilesMatch directive; and that takes priority over our attempts to use AddType or AddHandler for a directory.