Group Coupon Codes which assign a total value equally across payments

We offer payment plans for our programs.  As an incentive to pay-in-full, we add a small convenience fee to our payment plans. The more payments, the higher the fee. 

Occassionally, we run a promotion and want to offer a fixed amount discount.  We want that discount spread equally over the total number of payments.   Currently, Ontraport requires the coupon amount be applied in full to the first payment or repeated across all payments.

We don't want to create separate coupon codes for each payment plan option.  The only thing we can do right now is use a percentage and apply to every payment.  Those who select payment plans will get a larger discount than those paying in full, which is the opposite incentive we are going for. 

Having Ontraport divide out the discount and apply equally across all payments would be very helpful.