How do you opt into one software license and not the other when the distributor gives the consumer more than one choice?

For example I would like to use the DataTables JavaScript library in my web application. According to their web site, "DataTables is dual licensed under the GPL v2 license or a BSD (3-point) license."

Furthermore, the source code of the JavaScript library has this text that calls out both licenses:

/**
 * @summary     DataTables
 * @description Paginate, search and sort HTML tables
 * @version     1.9.4
 * @file        jquery.dataTables.js
 * @author      Allan Jardine (www.sprymedia.co.uk)
 * @contact     www.sprymedia.co.uk/contact
 *
 * @copyright Copyright 2008-2012 Allan Jardine, all rights reserved.
 *
 * This source file is free software, under either the GPL v2 license or a
 * BSD style license, available at:
 *   http://datatables.net/license_gpl2
 *   http://datatables.net/license_bsd
 * 
 * This source file is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the license files for details.
 * 
 * For details please refer to: http://www.datatables.net
 */

Finally, the web pages with the licensing text (e.g. the DataTables BSD license page) has this statement: "DataTables is made available under both the GPL v2 license and a BSD (3-point) style license. You can select which one you wish to use the DataTables code under."

My specific question is "how do you select which one you want to use." In my case, I want to only use the BSD license and I want to make it explicitly clear that I do not opt into the GPL v2 license in any way.

How do you do that and have it hold up to legal challenge?