I've successfully loaded the ID selector widget.
You can edit interface.php in your openid extension folder. Mine looks like this:
<p>
<label>Or login using your <a class="<?php echo $link_class; ?>" href="http://openid.net/">OpenID</a> url:<br />
<input type="text" name="openid_url" id="openid_url" class="input openid_url" value="" size="24" tabindex="25" />
</label>
</p>
<!-- BEGIN ID SELECTOR -->
<script type="text/javascript" id="__openidselector" src="https://www.idselector.com/selector/[myselector ID ...]" charset="utf-8"></script>
<!-- END ID SELECTOR -->
However, the css is not right. In Firefox and IE, the popup box covers the input box, which prevents you from entering a custom openID not in the list of providers. In Safari it works though.
I wrote to ID Selector people to see if there is a fix. You can reposition the button, but not the popup box.