Matt, for a while I was considering recommending Throw Dough
to aspiring pizzamakers as a potential launching dough analog, but the $30 price tag was a bit excessive and there's no way of knowing if it would act at all like regular dough on a peel.
The really nice thing about launching practice is that you can launch the same skin many times (on to the counter). You can make/buy a single dough ball, stretch it out, put it on the peel, launch it onto the counter, put it back on the peel and then repeat, over and over. Ideally, it might be good to have a well hydrated dough so it doesn't dry out too much as you're practice with it.
You probably don't want to practice with an actual pie that you're going to eat as the sauce might impregnate the skin as you're practicing and make it soggy and weak. It is important, though, that you mimic the weight of the sauce and the cheese. I'm leaning towards a pound of dried beans. The beans might have a tendency to fly off, but then, pepperoni has the same tendency as well.
With stretching, unfortunately, you can't stretch a dough ball, pull it together and stretch it again. You only get one stretch per dough ball. It's time consuming to make lots of dough balls, but at least flour is cheap, and even if you stretch the dough but don't bake it, it's not the end of the world. You could bake up a whole bunch of sauce only pies, so, if you do overdo it, you're not getting the caloric import from the cheese. Sauce only pies, without the cheese, should freeze beautifully.
Videos can help you make sure you're doing it right.
This is NY style (ignore the rolling pin/tossing stuff)
And here are some of the better videos for stretching Neapolitanhttp://www.youtube.com/user/pizzaiolopasquale#p/u