#include <Wire.h>
#define i2cAdd 4 //change to number between 2 and 4, assuming the mainboard is #1 in the I2C bus

void setup() {
  pinMode(4, INPUT);
  Wire.begin(i2cAdd);
  Wire.onRequest(requestEvent);
}

void loop() {
  delay(10);  
}

void requestEvent() {
  int16_t value = analogRead(4);
  byte array[2];

  array[0] = (value >> 8) & 0xFF;
  array[1] = value & 0xFF;
  Wire.write(array, 2);
}