Hi i actually did this hack 4 weeks ago, its quite ugly, but here goes:

Arduino 5v with external power and the sketch: https://github.com/mysensors/MySensorsArduinoExamples/blob/master/examples/RelayWithButtonActuator/RelayWithButtonActuator.ino

Connect the relay to gnd on the little controlboard and the first "long 30-min-spray solderpoint" just Connect some spare wire to test when the motor starts (it start after 15 seconds)
tadaa!

Use the pushbutton to start the airwick manually. i have a simple timer in domoticz that just shuts off the switch after 20 seconds.

This weekend i will build the MQ-2 sensor