Can PO Boxes be disabled using the widget?

Yes, the widget supports including the Address Autocomplete API parameters using the "address_params" option. We've created a small example showing this behaviour on the JsFiddle website.

The example shows the "post_box" parameter being passed through, but you can include any of the API parameters at this point (eg: you could also include "rural: 0" to exclude rural addresses).

  
    var widget = new AddressFinder.Widget(
      document.getElementById("address_field"),
      "XYU7FK4REMPDTWH3NQAV",
      {address_params: {post_box: 0}}
    );