just saw this today...sort of unrelated because it is smaller than a pizza box (just get 3 small pizzas? lol)
but it seems like you could use any ol' rack and 2 bungee cords and secure a pizza long enough for a neighborhood ride....

or in a more DIY fashion....

what if you just made some sort of flat board, pizza box sized (perhaps with ridges to keep the box in), that attaches to the flat of any sort of front or back rack?


also, i found this:

CETMA Style Bolt Together Front Bike Rack
http://www.instructables.com/id/CETM...ont-Bike-Rack/


didn't really peruse it much, but seems like a bike rack you can make yourself that dosn't require welding. bet you could fudge dimensions to make it more pizza box friendly....