I can heel toe half decently now (after lots of practice) and use it all the time on the street, makes downshifting so much smoother and quicker.
That said I never actually use my heel, elraton16 explained the way I do it too. Just use the center of your foot for both pedals, keeping your heel on the floor to pivot on. The ball of your foot controls your brakes, the small toe part of your foot controls the gas. Basically your ankle is what controls the modulation of the brake and gas.
I also have size 12 feet, so I don't think using my heel is even an option. Just becareful with the heel-toe when your shoes/pedals are wet, the last thing you want to do is slip of the brake and mash the gas when you're trying to slow down (as me how I know).
"Driving is like a narcotic, an addiction that can take over lives. It ruins people, breaks families apart, and even kills. Itís habit that needs to be fueled. Time, money, rationality, sweat, knuckle skin, and anyone who disapproves are of little importance to a driver, and are often overlooked. Hi, Iím Nelson, and Iím a drivaholic."