gistfile1.txt

You will need to locate a block with name "postbox_login_options_horizontal".
There, you will see that we create an unordered list (UL) with login buttons as
its items.

You will want to put your buttons just after the FOR loop (i.e. immediately
after the closing { /for }). Just make sure that your LI tag has class
"dsq-login-button".

  <ul class="dsq-login-buttons">
    { for option in loginOptions }
    { if option.enabled }
    <li class="dsq-login-button dsq-login-button-{= option.name }">
        <a href="#" onclick="return DISQUS.dtpl.actions.fire('{= option.action }');"></a>
    </li>
    { /if }
    { /for }

    {* Example of custom button *}
    <li class="dsq-login-button">
        <a href="#" onclick="changeMe(); return false;"><img src="path to button"/></a>
    </li>
    {* End of example *}

    <li style="clear:both"></li>
  </ul>