Membership Coupons: Only discount on sign-up not renewal

I have tried to set up a system using Membership to charge people 149,- each month.

However, I would like to offer a discount of 140,-, but only for the first month. I would thus want it to charge 149,- for the next months.

I have set up a coupon at 140,- to be applied to all subscriptions if used.

I have set up a subscription plan which is serial, period: 1 month and the price of 149,-.

When I apply the coupon it subscribes for 9,- pr. month, when I want it only to be 9,- the first month.

How do I come around this?