WSPBuilder per project configuration

When upgrading a custom SharePoint workflow recently I came across a useful feature of WSPBuilder, per project configuration.
WSPBuilder has its own config file WSPBuilder.exe.config which can be overridden in a visual studio project to provide custom settings for that specific project. All you have to do is add a copy of the file to your project from the installed location of WSPBuilder and uncomment any setting you want to override.