It's likely to help, but not necessarily completely effective. What you have to consider is that the condensation is continually forming whenever the car is sitting.

As an example, I was using our allroad at lot and my wife was driving our S4, which was only being used for short 10 minute drives (about 4 miles) twice a day. I too noticed a decent amount of white smoke starting to come from the exhaust whenever I was taking the S4 out. My mechanic checked the S4 and said there wasn't a head gasket leak - thankfully, but that it's condensation. He said not to worry about it, but that it's due to the car being driven only short distances. So I started to take the S4 more frequently to give it a good workout and the white smoke started to abate. I found that when I was cruising on the highway I would drop a gear or two and go full throttle, there would be a big white cloud, but after doing that a few times the white cloud would start to get smaller. I don't know for a fact this is the same issue for you, but you seem to have done your due diligence with your mechanic, so this is just what I think it sounds like.