Call your local pizza shop and tell them that you purchesed 3 large (chees, peporoni, ect, basically what you want on your pizza) last night for your (sons,nephews,neices,daughters, up to you) birthday party tonight. Then proced to explain how you just pulled them out of the (fridge,freezer) and they are (mushroom,chees, whatever you DONT want on the pizza) and be nice about it and say "i normally wouldent make a big deal but my son (or whoever yoru having the birthday party for) is allergic to (mushrooms or whatever) and ask for a replacement. Proceed to tell them that you can exchange the mushroom for the peporoni pizza. By LAW they have to say no as they cannot take food back. But the beneifit of this is to eliminate any doubt in their mind that you may not have really ordered any pizza. This method is efficent and works 100%. The only thing i advise against is doing it to the same pizza shop multiple times in to short of a period of time or they will catch on.
IT WORKS 100%