NULL Function in Calculated Metrics

I LOVE the calculated metric builder and I've started using some of the more advanced functions to start producing some much more useful interactive Workspaces. One wall I've hit though is that if I want to create a table of top products that match metric criteria such as "show me conversion for products with more than 1000 visits" when I rank in the opposite direction all I get is 0%. While this is technically accurate it means I can't create a table of those top products I'm just ranking the most relevant ones at the top.

The reason for this is the false value of the function is 0 which is still interpreted as a value and therefore displayed in the report, what I want to be able to do is set it to NULL instead so that if I sort by that metric ONLY those products are displayed and everything with no value is hidden.