Both your ideas should work. I don’t know where your model is geo-located. When I start a new Sketchup model, it defaults to the Denver Colorado area. I can then use a dialog box (Shadows tray in SU 2016) to change the time of day, which re-positions the sun. I can also use that shadows tray to change the day of year. If I set the month to July (summer in the northern hemisphere) and a set the time to either early morning or late in the evening, I can set the shadows so that they have a south component. Is that good enough?
To really make shadows fall to the south even more, I geo-located to Sydney Australia. There I can make a shadow fall due south. On the other hand, you may just be easier to rotate your model 180 degrees.