Load up the race track 'Coco Park' (eg. in a single race, cup or adventure) and you then need to drift continuosly (15 seperate). They do not need to be boosted thus you can just do 15 quick drifts in a row and Coco Park is perfect to do this as the map is large, wide and perfectly made for drifting.
I made this video to help:
Hope this helps.