If your page doesn't need to use any of the order data we append to your URL after the ?, your site's landing page can simply re-redirect to another, final landing page -- e.g., suppose your Common Thank-you Page URL is http://www.example.com/redirect.html, then the HTML on that page would be simply this:
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="refresh" content="0;url=http://www.example.com/thankyou.html" />
</head>
<body>
<a href="http://www.example.com/thankyou.html">Click here to proceed</a>
</body>
</html>
...where of course http://www.example.com/thankyou.html is the URL of your final landing page. The "Click here to proceed" part is just in case the buyer has blocked such auto-redirects in their browser, but normally this redirection should happen instantly.
