Need help with Taxable vs Nontaxable discounts on invoices.

SUGGESTED

Hello, 

We are trying to set up an invoice report for a 3rd party company to help us manage our taxes. They require that we put taxable amounts on one row, and non taxable amounts on another row per invoice as we have some invoices that have both taxable lines and non-taxable lines. 

Since the discount amount for the invoice tables is on the header, I'm having trouble determining which line (taxable or non-taxable) to associate the discount with. 

For example:

Invoice ABC-123 has one taxable line of $50 and one non-taxable line of $75. The invoice also has a discount of - $25. This brings the invoice total to $100:

Taxable Total = $50, Non-Taxable Total = $75, Discount = $-25, Net Invoice = $100

How do I determine which of the two below lines is correct?

1) Taxable Total = $25, Non-Taxable total = $75

2) Taxable Total = $50, Non-Taxable total = $50

I would prefer to avoid UDFs/Scripting for time purposes, but I am not seeing any way to tie the discount to a specific itemcode/line on an invoice. 

Any help would be greatly appreciated!