The Crew

A very good car for the Stunt Combo is the Ruf CTR-3, which can be bought at the dealer in Miami. If you don't have enough Bucks, you can proceed through the story until you can join a faction and get 100 000 CC as a gift.

Drive to the Bonneville Salt Flats and use the big flat area to drift from combo to combo. You only need to steer left and right to get a drift going. No need to use the handbrake.

Update: Jan 1/15
Seems like they patched it so that you can't get any bucks once you reach multiplier x2, but you will still get the achievement.
Thanks to SR1 Dan for confirming :)

The previous solution worked pretty good before they patched the way combos work. Apparently the solution is still working but I had a hard time keeping the combo going after it reached 2x, so I found a much easier solution.

Go to the world map. Press RB/LB to get to the Skills menu. Select the Speed Skill 83 at the very south of the Bonneville Salt Flats (North of Las Vegas) and do a fast travel.
From the starting point, move back a little and choose one of the lanes of traffic cones. Just drive over them in a straight line with about 100km/h (~60mp/h) and you should get the achievement at the very end of the lane. To make sure you get it (especially if you're faster than 100km/h or 60mp/h), you can add a drift or two after you left the last cone behind.

The by far easiest way to get this is to find a long stretch of fence - they're everywhere in the East Coast countryside. Just drive slowly along the fence, wrecking it, and you will get the achievement in no time... well in a minute actually. Just ignore the rating calling it "boring" towards the end.

On the East Coast west of New York there is an area called "Pit Mines." The dirt roads leading up to it are lined with breakable wooden fences. I got the achievement by getting a continuous "Collateral Damage Skill" by driving through the fence line.

Just a note. After a while the notification will say "boring" and stop awarding you points, but it will keep the streak alive.

After trying the two methods above for over 2 hours today with no success, I tried something different and it popped first try!

Maybe they patched it again with the new update coming out yesterday, who knows.

Anyways, take your highest leveled Circuit Spec car (mine was a Nissan 370Z at lvl 1200) and go to the Salt Flats.

Now speed up to ~160 km/h (100 mph), hold your speed and steer to one side until you slightly drift. That's it, hold it for a minute and it should show you the golden message in the bottom right of the screen and shortly after the diamond toast pops.

Hope it helps!