I've never managed to finish a 24 or a 12 helmeted: I've done three 24s and four 12s, of which one 24 and two 12s had me wearing a helmet at the start; I ditched the lid in the latter stages of the 12s and about halfway through the 24 - I always get Shermer's Neck. I've never spent the whole time in the tribars either.
I guess I could wear a superlight road helmet, but those things are parachutes. I could also do super-Rambo style core exercises for six hours a day every day, but it's not like I've never tried that before. My PB is close enough to the limit of my ability, and the work and resources required to stand a good chance of beating it are high enough, that I'm not prepared to try it if I've got a sword of Damocles hanging over my neck in an aero lid, nor if I've got to shoot myself in the aerodynamic foot, especially not for the sake of some stupid, scientifically-illiterate rule. Retirement it is then, I guess.
Good luck LWaB!