Yeah I've found that the handbrake only really works in low speed situations with the tiptronic. The only thing guaranteed to work is power power and more power.
The thing is that our cars are set up to be stable, the 4 door even more so than a 2 door, so you need heaps of power to keep it out there unless you modify the suspension properly.
I can do it a bit on certain corners (I have witnesses to my 4 wheel drifts on the last turn before the straight at Wakefield) but really all I'm doing is going into the corner too fast, hitting the brakes while turning to get the back end out and then using the power to keep me drifting. I dunno if this counts for the purists out there though.
In fact come to think of it, except for pure power oversteer, that's about the only way to do it.