This is now solved 
though slightly differently to how it was asked for.
Rather than padding the sheet with a line for everything you currently hold none of, the new on-screen stock take has an “Add a row” button. When you find stock that isn’t listed, add a row for it there and then, and Breww asks only for what it needs for that particular item. There’s a “Save & add another” option too, so you can work through several finds in one go without picking the location again each time.
We went this way because a brewery with a lot of dormant items would otherwise face a very long sheet of zeroes to scroll past, which made the count harder rather than easier.
Adding rows is covered here: Breww | Counting a stock take on screen | Help guides
More on this and the rest of the update here: Stock takes just got much easier to run