RewriteEngine on
RewriteRule ^static/.+.(js|ico|gif|jpg|jpeg|png|css|swf)$ compress.php [NC]

<?php

$basedir = realpath( dirname($_SERVER['SCRIPT_FILENAME']) );
$file = realpath( $basedir . $_SERVER["REQUEST_URI"] );

if( !file_exists($file) && strpos($file, $basedir) === 0 ) {
    header("HTTP/1.0 404 Not Found");
    print "File does not exist.";
    exit();
}

$components = split('.', basename($file));
$extension = strtolower( array_pop($components) );

switch($extension)
{
    case 'css':
        $mime = "text/css";
        break;
    default:
        $mime = "text/plain";
}

header( "Content-Type: " . $mime );
readfile($file);

$basedir = realpath( dirname($_SERVER['SCRIPT_FILENAME']) );
$file = realpath( $basedir . $_SERVER["REQUEST_URI"] );

<Directory /data/www/path/to/some/site/js/>
    AddHandler application/x-httpd-php .js
    php_value auto_prepend_file gzip-js.php
    php_flag zlib.output_compression On
</Directory>
<Directory /data/www/path/to/some/site/css/>
    AddHandler application/x-httpd-php .css
    php_value auto_prepend_file gzip-css.php
    php_flag zlib.output_compression On
</Directory>

<?php
    header("Content-type: text/javascript; charset: UTF-8");
?>

<?php
    header("Content-type: text/css; charset: UTF-8");
?>

$p = 'path/to/css/file'
$i = stat($p);
if ($_SERVER['HTTP_IF_MODIFIED_SINCE']){
    $imd = strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']);
    if ( ($imd > 0) && ($imd >= $i['mtime'])){
        header('HTTP/1.0 304 Not Modified');
        header('Expires:');
        header('Cache-Control:');
        header('Last-Modified: '.date('r', $i['mtime']));
        exit;
    }
}
header('Last-Modified: '.date('r', $i['mtime']));
header('Content-Type: text/css');
header('Content-Length: '.filesize($p));
header('Cache-Control:');
header('Pragma:');
header('Expires:');
readfile($p);

gzip -c styles.css > styles-gzip.css