C.O.D payment by %

So, Im having a little trouble setting up a new way of payment that in my country works like a beauty.

C.O.D Cash On Delivery.

So I have this seted up with an extra 5€ surchage.

But I do need for the customer to pay 60% of the total value of the order.

This means in a 100€ order the client pays 60€ and the rest (30€ + 5€ of the surcharge) on deliver.

So how can I make this option available on the invoice so that the invoice shows up with the total value and the 60% that the client needs to pay once choosing the C.O.D payment method?

Any help is higly appreciated.

Im bumping this thread because I really need this.

According to my knowlage this is a simple taask to do, I jsut dont know how to.

This must only tell client that he should pay 30% so its simple math programmed on invoice using the total amount to be paid buy the client