Gotta love these late nights. I got it - a simple div wrapper:

$content .= '<!-- (c) 2006. Authorize.Net is a registered trademark of Lightbridge, Inc. --> <div align="center"><div class="AuthorizeNetSeal"> <script type="text/javascript" language="javascript">var ANS_customer_id="---------";</script> <script type="text/javascript" language="javascript" src="//VERIFY.AUTHORIZE.NET/anetseal/seal.js" ></script> <a href="http://www.authorize.net/" id="AuthorizeNetText" target="_blank">Online Payment Service</a> </div></div>';