Oh!, Ok...I mis-understood your final goal (I think your the only one that hasn't wanted to sneak in a couple of extra fish). Put a layer of scrubbies under the top layer of bio-balls, it will get them started faster (don't leave it off very long (10-20 min.)). And like I said the bacteria will grow to the space needed to feed on the waste. Don't over-feed, it just puts garbage in the filter and promotes an algae bloom.
Watch the chemistry (take a reading before you change anything as a bench mark. Then check every week, when the numbers stabilize at their lowest for a couple of months your there (if still not low enough after a few months add another layer if there's room).
No more fish huh? Are you sure?! You know we can use google satilite to check...