Technically, what that driver did was illegal since (assuming a passing zone) you're only allowed to attempt a pass using an oncoming lane when that lane is clear for the duration of your maneuver which clearly it was not because you were there. Of course that won't be of much solace if you happened to have been merged with the grillwork of that car. Aside from changing your route, I suppose several things you can do is start carrying a horn or keep a high-powered light mounted and use it to signal to the driver that you are in the lane. Other cars will flash their lights at cars attempting to pass using their lane when they think the oncoming traffic is cutting it too close.

BTW, a similar thing occurred to me last weekend although I wasn't on a bike at the time. I was in the car with my wife and we were in a long line of cars all doing the speed limit when a car passed us in the oncoming lane. There was no room in front of us or even for the next 5 cars so he passed us all and got to the front where he was about three car lengths behind more traffic. He then attempted the same maneuver. We lost sight of him doing probably 85MPH up the road. However, that was not the last time we saw him. We passed him about 20 minutes later where he was stopped off to the side of the road waiting as the officer in the unmarked police pickup truck was writing up his citation.