Ok here's how it goes...
1. put in manual mode (for those who have dct)
2. put in sport +
3. press brake
4. floor the throttle. the engine speed will be establish (i think the rpm will hold at some number). Then in the instrument panel will show a little checked flag.
5. let go of the brake but keep the accelerator floored. (gearbox will shift up automatically).
(as long as you've keep flooring the throttle then launch control will kick in. The idea is for this to work you have to floor it)
Just don't do it too many times. Will be nice to try out though.