Triggering a drive-through penalty only works when you set the rules and flags to realistic and set the race distance to 20% or more, as the game is programmed to only give time penalties under this distance.
Since the achievement requires you to win the race, I would advise you set up another Custom Grand Prix online session and invite a friend. Set up the race in any way you want, only make sure to select 20% racing distance and set rules and flags to realistic and damage to cosmetic, just to be sure.
As soon as the race gets underway, start cutting corners wherever you can. Simply cut every turn and in a matter of 1-2 laps maximum you should receive a drive-through penalty. Serve your penalty and let your friend give you 1st place, then simply finish the remainder of the Grand Prix.