I have checked out the labels for several bake-to-rise frozen pizzas on the market and, to the best of my recollection, most of them include a combination of yeast and an encapsulated leavening system such as WRISE, which is a commercial product of the Wright Group and composed of partially hydrogenated cottonseed oil, sodium aluminum phosphate (SALP) and sodium bicarbonate (baking soda). Many take-and-bake refrigerated (not frozen) pizzas, including many sold in supermarkets, use the same or similar leavening system. The frozen pizzas sold commercially in supermarkets are flash frozen at very low temperatures. The chemical leavening system kicks in only when the internal temperature of the pizza as it bakes rises to a prescribed value.
Tom Lehmann discusses the idea of making frozen pizzas at http://thinktank.pmq.com/viewtopic.php?p=2330#2330
, and also in the audio segment dated August 30, 2006 at http://www.pizzaradio.com/Index.php?paged=6