Get your own domain and make a folder called 'whatever' then make a php file call index.php past this code into it...
Change the example URL to your affiliate URL.
PHP Code:
<?php
header( 'Location: http://www.example.com/?aid=38384' ) ;
?>
Save that as index.php
Now you need to upload index.php into your 'whatever' folder.
That's it your done.
If you do that right you should have a cloak that looks like this
www.example.com/whatever redirects to
http://www.example.com/?aid=38384
Hope this helps!