<?php

umask(0);
$file = tempnam(sys_get_temp_dir(), 'PHP-Test');
chmod($file, 0777);

$class = <<<FILE
<?php

class MyClass
{

    public function testMyAss()
    {
        echo "some content";
        echo "some other content";
    }

}

FILE;

echo highlight_string($class, TRUE), "<hr>\n";

if (file_put_contents($file, $class) === FALSE) {
    die('shit maaan :(');
}

require_once $file; // create class

function appendToMethod(ReflectionMethod $method, $content)
{
    $file = fopen($method->getFilename(), 'rb+');
    echo seekLine($file, $method->getEndLine());
    fwrite($file, $content);
    fclose($file);
}

/**
 * @return string|FALSE
 */
function seekLine($resource, $lineNumber)
{
    rewind($resource);
    for ($i = 1; !feof($resource) ;$i++) {
        $line = fgets($resource);
        if ($i === $lineNumber) {
            fseek($resource, -strlen($line), SEEK_CUR);
            return $line;
        }
    }
    return FALSE;
}


appendToMethod(new ReflectionMethod('MyClass', 'testMyAss'), "echo \"my ass\";");
echo "<hr>", highlight_file($file, TRUE);