domain1.com/index.html
<script type="text/javascript" src="http://domain2.com/show.php"></script>
domain2.com/show.php
document.write('<div id="0123456789"><script type="text/javascript">google_ad_client = "pub-1234567890";google_ad_slot = "1234567890";google_ad_width = 160;google_ad_height = 600;</script><script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script></div>');