scons GUI=wx [WX_VERSION=##]
Where WX_VERSION is the two digit representation of your wxWidgets version. The 2.6.x series would be 26, the 2.8.x series would be 28, and etc. The default value for WX_VERSION is 28. The value of WX_VERSION effects the name library files generated during the build as well as the names of the wxWidgets libraries that the wxWidgets demo will link against.