Best place for Mercedes i know in Dubai after Gargash is Mercedes R us in Rashidya, google there number and check with them if they can install such option. There is another VIP german garage in rashidiya as well, but be clear with them as i have heard some dramatic story of inflating price after job is done and customer is in no position to argue or bargain other then just pay. So if they say they can do that, get that in writing or on email and stick to the agreed price.