The target is moving in a convoy. Take a good handling car and drive up towards the target. The convoy is a stretch and two SUVs. If you are in a helicopter, slowly and methodically crash into the limousine, which pretty much makes it undriveable, and then just drill everybody with your SMG or Carbine Rifle. Another way to stop them is to get ahead of the limousine and through a Grenade outside of the window, this will stop the convoy and if you time it just right you will even be able to blow up the convoy and the target as well. You can also block the target's way with a car rigged with Packie's bomb and detonate it as the limo gets close. This requires a good timing, though.
