Zen Cart 1.3.8a

Currently using the "Discount Qty Applies to Mixed Attributes".

The pricing has already been set by our customer, and the only options available are Percent/Acutal Price/Amount Off.

I want to have buy 10 get 2 free & buy 20 get 2 free applied to product/gift certificate.

Price per item = $78.00

qty. x10 = 780.00
qty. x20 = 1560.00

With both of the above i want to add qty. x2 free. With the options available the numbers do not work out evenly... Any Help with this?

(*I have seen some threads close to this topic, but not exactly, and I detailed out my issue. Did I get this post in the right thread?)