Minimum UNITS to qualify for Salemaker discount.

Hi all. How can I set a minimum UNITS quantity of a single item to purchase to qualify for a Salemaker discount? I see price range (ie. minimum $10), but what I need is minimum number of units (ie. 5 of the same item).
I want to apply this to an entire category, in our case fabric, so Salemaker seemed to be the way. Customers can purchase fabric in 0.05 metre units, with a minimum 0.1 metres and that has been set up correctly. But if they purchase 0.5 metres or more, I want to give them 10% off. If they purchase 0.5 metres of one fabric and only 0.25 metres of another, they'll get 10% off the first one but not the second. And no discount on items from any other category that they may buy as part of the same order (ie. thread, needles, etc.) And since price per metre ranges per fabric, can't just fake it with a generic price guesstimate.
Is there a way to do this natively? Or a hack to add an additional condition to whatever PHP files/SQL query calls the Salemaker query (ie. includes/functions/salemaker.php)? Or am I looking at adding a plugin?
Thanks!

You can do this sort of thing with my Quantity Discount plugin. It's in the Plugins area at the top of the page.