-DWHIZARDas the third argument to cresgvexe. Copy the most appropriate steering file from SGV_DIR/samples/whizard to your private area, and link it to unit 17. SGV in whizard1 mode can set many, but not all, whizard input variables, so You will probably need a whizard.in file to steer whizard.
SGV_DIR/samples/whizard also contains two examples of steering files.