There are many types of solutions available using an arduino. The hardest part would be accessing the contacts on the back of the necessary buttons to break out leads to attach to the arduino.
You could use an IR sensor to make the controls accessible to a simple IR remote.
Also you could use one of many types of light sensors to even automate dimming based on light level in the vehicle. The arduino would not be able to sense what state the monitor menu was in so you would have to experiment with timers in the code to handle the multiple external button presses to build sort of a "macro" for brightness up and down.