Technically the switch is not complicated at all. It just needs to be a momentary switch, like the 'reset' button from a computer. The install is fairly simple in that you really need to put just one wire into a control module, the other wire is to be connected to ground (car chassis).
You can get the OEM EV button, but it's rather expensive, so it's up to you. Google around for some instructions (should be a PDF) with pictures and diagrams from the service manual.
The main advantage of using the EV button is that it can prevent the engine from coming on when you start the car, just push the button before
the engine starts. This can help mitigate the warmup penalty, especially if you just want to move the car a little. Of course it's always fun to use it when you want to show off stealth mode to people.