For the default PS3 controller, I'm afraid it doesn't work and you may be stuck with the original d-pad.You'll probably need to buy a modified PS3 controller that might have possibility to change the Analog system.
I don't have a PS3 either way so that's my best help.
You'll have to push the PS button and go to controller settings and set it to Analog before the start of every race, while it's on the race screen counting down to the start of the race. That's the only thing that works for me. It resets to Digital once you exit the race. Very annoying.