So, I found a new spot that's absolutely perfect (thank you, Google Earth). So perfect that two guys were down there racing with GoPros mounted on their roofs...
Long stretch in an industrial park with a dead end.
The winning combination seemed to be long-pressing the DSC button to completely turn off DSC.
0-60 time was 4.57 sec. I also kept my foot on the brake until I had floored the gas to prevent the accelerometer from starting the clock prematurely (that alone didn't make a difference in launch time when I tested, for the record). I had no noticeable fish tailing or wheel-spin.
As for starting in second, I noted that Sport+ does indeed start in second, FWIW.
In other news, the Dinan stage 3 ECU and intercooler install is scheduled for Thursday, so I should have new numbers by the weekend.