I too am able to do it , but i loose on speed on the later part of the game and hence i an not able to score max.
Speed is the only way to get high drift scores.
frankly speaking in my 4M drift i have got max points in the start of my race on GVR later i earned very less drift
points as i am not able to maintain the speed.
1st - 1XX,XXX in 20% of the game.
2nd - 1XX,XXX in 80% of the game.
That made me reach 4M i am trying to increase that 1st part to get high drift score.
The key is good controller , high speed , Viper SRT 10 , manual gears.