i taught a young lad who had a very flat swing. he would have his left arm on the same line as his shoulders at the top, and fire his hips early, drop the club even flatter and roll his hands over very quickly. still took divots in front of ball and it pretty much went were he was aiming and was playin off about 9 at the time. i stuck his umbrella in the ground along the target line about a yard 1/2 down the line, not on the target side, and aimed it pretty much to his shoulders. told him to swing outside it goin back, and swing down under it on the downswing. hits hit full distant drivers goin outside the umbrella ... and back underneath the umbrella. his top of backswing whilst he did this looked very weird, but it worked. straightened out his hook, and made his backswing more upright.
so if you hook the ball, it can be a good way to straighten it out.can also wrk if your a slicer, becuase you have to swing towards the inside of the ball.
i believe its the vijay drill