Hello J_Miller79,
Yes, you can certainly use sourdough scraps or discard to make kvass, and it is actually a wonderful way to avoid food waste while saving money. While traditional Russian kvass typically relies on dried black rye bread and fermented malt, wild yeast from your starter will still produce a tangy beverage.
To get closer to that authentic flavor profile, I recommend baking your sourdough scraps until they are deeply toasted. Combine your toasted scraps with water, sugar, and a bit of active starter, then let it ferment for a couple of days.
It is quite easy to make and yields a refreshing, probiotic-rich drink.