Elaboration as to why you cannot (as I understand it) . . .
Commercial yeast (be it brewer's yeast, IDY or ADY; their all the same organism) was selected as the commercial yeast used today because of its strength (excellent rising capabilities), predictability, and because of its ability to live for long periods in a non-acidic environment, making it easy to transport, store, etc. Conversly, commercial yeast cannot live for very long in an acidic environment, the exact opposite of wild yeast. But, alas, it is the acidic environment produced by lactobacili that give bread/pizza great flavor. Wild yeast can continue to live forever -- as long as you keep on feeding it flour and water -- because the yeast and lactobacili live in a symbiotic relationship: each is essential to the other's survival. The big problem for creating a starter from commercial yeast is that over time it creates the very same environment that it cannot survive in; in a sense commiting suicide. As the yeast ferments the flour, it increases the acidity of the mixture, killing itself off, leaving a paradise for some stray wild yeast/lactobacili couple to multiply and conquer.
Just a final point, even if making a starter from commercial yeast could work, there would be no benefits to the dough; it wouldn't taste any better. You would, of course, not have to buy the yeast again, and that is a benefit to your $dough$.
Hope that helps. And if I'm wrong, please somebody correct me. Thanks.
