Unless you've got a JDM and then you've got no idea what they are for   
  
If you've got a spare switch position next to the heated seats you could use that with a "standard" switch with an icon on for heated screen or something. If you have the 02-06 model, just be careful not to hit the "secret" switch with your elbow when changing gear, Zeds don't handle well if the engine is suddenly killed   Might be better to put it by the ESP button (where the roof switch position is in a roadster)