Here's tips on how I got this achievement:
First, change the 3-point sliders in your favor; that's a given. Also, make sure that the quarter lengths are set to 6 minutes and Pro difficulty (thanks NiteJokester). Now, whenever you attempt the half-court shot, the key is to press Y to get in the post and shoot from the post position while slightly fading away (on some attempts I just shot it with the X button without fading away; it rimmed out on a few of these attempts). The reason for this is because by doing this, the player will actually accurately aim for the shot as opposed to just throwing it up towards the basket. Thus, this increases the chances of making the shot.
So, during my game, I let the defense score purposely on every possession to speed things up. Then, while on offense, I dribbled to center half court. Before crossing the center line, I hit Y to go in the post position and shot it from there. It's hit and miss so you're not gonna get it the first time. However, I hit either hit the rim or had it rim out as opposed to an air ball. I finally got it during the 2nd quarter of my game. Hope this helps.
Update: Per Madtown B, this may be glitchy in MyCareer as hitting a half court shot did not unlock for him. I did this in a regular exhibition match.