Dwight Howard plays for the Orlando Magic, so play as them. You can combine this with the "D12 11/12/08" achievement, which is 10 blocks with Dwight Howard against the Oklahoma City Thunder (be sure to play as the Away team for that achievement).
Set player lock on Howard before the game and turn all fouls off. Keep Howard under the basket on your own half of the court. When a player tries to shoot, press Y to jump and block his shot. It's a little tricky, and timing is key, but with setting the game to 12 minute quarters, you'll give yourself PLENTY of time to get it.