I buy marinades. Take 4 pounds of chicken and dump it into a big tupperware container. Then take an entire bottle of marinade and dump it in.
Obviously the type of marinade is important; extremely important. Currently, the marinade I use is 10 calories per serving, 32 servings per container. It's the "Zesty Savory" marinade from Wegmen's. Of the 4 pounds of chicken, there are usually around 32 pieces of chicken. Since some marinade is left over I just assume 8 extra calories per piece of chicken. The marinade I use has no fat, just carbs. So I've added 2 carbs per piece of chicken, but I've gained a metric crapton of flavor.
I like to marinade the chicken for 2 days in the fridge. It syas marinade for 30 minutes but you have to let it really sit for over a day to let the flavor soak in more fully. Once it's been marinading for 1-2 days, I grill all of it at the same time and put the cooked chicken in a different tupperware container.
There is a better marinade I used to use. It doesn't taste as awesome, but it's only 5 calories per serving, and only 24 servings per container. So you wind up adding about 0.5 grams of carbs per piece of chicken.