GPL License with Modified "Beer Clause"

When I was working at UC I got interested in random number generators for a while and came across an interesting test suite called "dieharder" which evaluated random number generators and looked for common flaws. This software was written by Robert Brown (a professor at Duke), and it contained one of my favorite software licenses of all time. The author described it as a "GPL license with a modified 'beer clause'" or as "GPL version 2b (b for beverage)". The license basically requires anyone who uses the software to offer to buy the author a beer if they ever meet him in real life. This is the type of license I'd like to include in my own work.

The text of the license (ast least, as best as I can find it today) is:

License: GPL
On Debian GNU/Linux systems, the complete text of the GNU General
Public License can be found in `/usr/share/common-licenses/GPL'.
The main copyright statement is in copyright.h:
 /*
  * $Id: copyright.h 256 2007-01-27 15:14:15Z rgb $
  *
  * Copyright (c) 2003 by Robert G. Brown, rgb@phy.duke.edu
  *         GPL version 2b (b for beverage) granted as given
  *         in the file COPYING in this distribution.
  *
  * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
  * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
  * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
  * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
  * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
  * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  * PERFORMANCE OF THIS SOFTWARE.
  *
  */
The bevarage clause mentioned is
   License is granted to build or use the accompanying software:
                             dieharder
  according to the following standard Gnu General Public License or any
  later versions, with the one minor "Beverage" modification listed below.
  Note that this modification is probably not legally defensible and can
  be followed really pretty much according to the honor rule.
  As to my personal preferences in beverages, red wine is great, beer is
  delightful, and Coca Cola or coffee or tea or even milk acceptable to
  those who for religious or personal reasons wish to avoid stressing my
  liver.
                  The "Beverage" Modification to the GPL
  Any user of this software shall, upon meeting the primary author(s) of
  this software for the first time under the appropriate circumstances,
  offer to buy him or her or them a beverage.  This beverage may or may
  not be alcoholic, depending on the personal ethical and moral views of
  the offerer.  The beverage cost need not exceed one U.S. dollar
  (although it certainly may at the whim of the offerer:-) and may be
  accepted or declined with no further obligation on the part of the
  offerer.  It is not necessary to repeat the offer after the first
  meeting, but it can't hurt...
which is followed by the text of the GNU GPL, Version 2, June 1991