How can you sell a "remainder" stock that is a part-pack?

If i set up a product with a box qty of 24. And I only have 3 in stock, how do i get rid of those last 3? There ought to be an option that allows you to sell a "remainder qty" below the minimum pack size.

This should also work if there are 27 in stock - i.e. i should be able to sell one box, plus 3 individuals (even if i cannot normally sell the 3)