Free shipping after 3 products added to cart

-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.3
-- PHP version -- : 5.4.45
-- Browser(s) name and version -- : Chrome

I would like to offer free shipping after someone adds 3 products to their cart. I use the USPS Shipping Module. I tried the Shipping Method Restrictions feature, and entered 3 in the Maximum field. That obviously gave me a "No Shipping Method Found" after increasing the number of items to 3. I realize that I need to create another Shipping Method with a Minimum Restriction of 3, but what I cannot figure out is how to offer this method for free keeping the USPS format for those that would like to track their order? Is creating the second shipping method to Manual Shipping my only option?

Thank you in advance.

Thank you.