Take a look here:
http://www.realoem.com/bmw/enUS/show...diagId=34_2208
It shows that the parking brakes are very small mechanical drum brakes. Having seen this system in person and having worked on it on my E90 I can tell you it is not remotely set up for drifting work. It's designed for what it is normally used for, use if for drifting and you will screw that system up. I don't know about the DCT but I suspect the rear diff won't be happy if you start doing handbrake turns, on the ice will reduce these factors a bit but I wouldn't do with the stock system.