S-Tronic Diesels do have lauch control!
Having previously tried many times to get launch control working on my TDI 170, I came to the conclusion it wasn't implemented on the diesel models.
Correction - it is!
...and your tyres will not last long with it either.
What was happening was that the car was bogging down when trying to initiate the launch control procedure and the revs would return to idle. I've found that if the car moves even an inch forward whilst you're trying to do a launch, the car won't go into launch mode and it bogs down.
Here's the procedure:
Push the brake pedal down *as far as it will go* - I was not doing this previously so the car was able to move forward and not engage launch control.
Throttle to the floor
Petrol cars rev up to 3500 odd rpm, the diesel will rev up to 2000 rpm and hold steady waiting for you. When you're good to go, release the brake pedal and you're off. You can make really good getaways with this, but I was having trouble with traction today (although it was cold and the roads damp) - as soon as I hit 3000 rpm I'd break traction. Even so, 60 comes up in not much time at all.
Have fun, guys!