Clickbank doesn't have a 6 months billing option?

Hi all,

I'm trying to setup a new site for a new IM membership site.

I want to charge the members monthly and for 6 months upfront with a big discount.

However clickbank doesn't have the 6 months option on recuring billing.

The only options they have is biweekly, monthly, quarterly and 12 months.

So anyone have any suggestions as to how to have a every 6 months recurring billing through clickbank?