I do it all the time. I did it tonight. Rode half a mile through residential with an 18 incher on my beater mtb with no hands on the bars. I do it like a server at a diner would do. One hand in the center of the bottom of the pizza box.

I however have an amazing sense of balance and can ride for miles even taking turns without hands. I have actually thought of making some kind of plastic carrier box for the rear of the bike lined with a material like a pizza delivery guy uses. !8 inches of pizza, or could carry 4 to go containers.

Maybe i'll do a vid tomorrow of how to do it