You can get ASC+T (traction control) by getting the MTH engine map upgrade (150 euros I think)
You cannot retrofit
DSC (Stability control) on a car that didn't come with it, you need extra sensors.
The difference between ASC and
DSC are listed under the Mini 2 faq.
You do not really NEED traction control, I've driven 5 years in Calgary (snow on the ground 5 months a year) without traction control, so does most people out there, just don't step on the throttle like a mad man, you'll do fine. Practice on an empty parking lot or something so you're used to it.
Search for "snow" on the forums, lots of threads about snow driving.