Coupons under ProSites

Got a question...
I Setup a coupon for someone today and was going to give them 50% off the first month and then they would pay the regualr ammount from then on.
When I set the coupon up there was no place to to specify the 1,3 or 12 month on the list and as expected, when I made the coupon it took 50% off all three options which is not what I wanted to do at all...

Is there a work around for this? or am I missing something?
Thanks for your help