I already know how to do it...and the solution in your post only covers part of the issue. WSPBuilder does not support .net 4 framework, which is the main issue because you need .net 4 framework for SharePoint 2013.
From: Matt_Bezanson [email removed]
Sent: Friday, March 15, 2013 5:45 PM
To: willzworld2@msn.com
Subject: Re: I Have the Solution to Make WSP Builder work with Visual Studio 2012 and SharePoint 2013 [wspbuilder:404783]
From: Matt_Bezanson
Here is a post that talks about how to do this:
http://gblsharepoint.blogspot.com/2013/01/using-wspbuilder-with-visual-studio-2012.html
Note the path in Win 2008 R2 is: C:\ProgramData\Microsoft\MSEnvShared\Addins