I've got 4 in that spot on mine too, I have 2 double USB outlets in the 2 spots under the instrument cluster and 2 more switches in the spot just under the air vent on the driver's side next to the steering wheel.
You could probably fit one down near the heat switch in the lower panel there, but you'd need a smaller switch as the Carling sized ones that fit in the other spots are too tall to fit in there.
The only thing I found with the spot near the driver's side vent is that because it is so deep, the switches don't clip in there. I just put a drop of superglue on the little tabs on the top that usually clip inside the panel (like they do on the bit near the hand brake) and they haven't moved since I put them in there probably 6 or 7 years ago...