How to PREVENT fishtailing?

Sorry, but thats not a good car for bad weather. No way to control the loss of traction other then different tires. You have a much to aggressive tread pattern on those high performance tires. A good step is to get a second set of rims and tires for winter driving. Look for "all season" or " M+S" (mud & snow ) in the tread guide. The Tire Rack as options for all high performance cars with that problem. Your car was meant to be driven in bad weather.