I got this working on Xenforo 1.3 by adding this in the Foolbothoneypot_register_form template.
Code:
<dl class="ctrlUnit">
<dt><label for="ctrl_location">{xen:phrase location}:</label></dt>
<dd>
<input type="text" name="location" value="{$fields.location}" class="textCtrl" id="ctrl_location" />
<p class="explain">{$xenOptions.MandatoryLocationPhraseRegLoc}</p>
</dd>
</dl>
On default xenforo you would add this to register_form
The reason it wasn't working for me before is because the template modification in this addon was trying to find and replace: <dl class="ctrlUnit OptOut"> which is no longer in the latest versions of Xenforo.