Has anyone set up payment terms with a discount based on due date, not invoice date?

Here's the scenario:

Vendor payment terms are a fixed date several months in advance and are not based on invoice date. Multiple invoices within a several month window can have the same fixed future due date. Discounts are offered "in anticipation" of the due date, with a 0.5% discount granted for each 30 day period the invoice is paid in advance of the due date.

Example: Two different invoices are received, one dated January 5th and the second dated February 10th. Payment terms stipulate that both are due June 15th, and grant a 0.5% discount for each month the invoices are paid in advance of the June 15th due date.