coastmediagroup

What I am looking for is this: On invoices sent to customers for hosting I want to be able to encourage customers to renew their hosting for 2 or 3 years i.e. Biennually and Triennually. These options are set up in WHMCS. However they are only able to be used on ordering rather than renewing. So in essence I want to say on the invoice "Save 25% by renewing for 2 years" etc. Has anyone done anything like this? Mike