An approach you might consider would be to use an analog pin instead of digital. Presumably, when the switch is pressed, input voltage is very nearly 5v. So you could do something like:
const int pinNum = 0;
const int pressedThreshold = 1000;
void loop() {
int a = analogRead(pinNum);
if (a > pressedThreshold)
tune = random(1, 5);
}
You might have to tweak the pressed threshold a bit.