Setup fees are a one-time transaction charged automatically at the beginning of a subscription billing cycle. There is not currently a way to create a coupon to specifically waive a subscriptions set up fee. Set-up fees cannot be edited at the time of subscription creation.
One option would be to create an identical subscription plan without the set-up fee. For example if you have Plan A "Premium 3 Months" ($50/month +$30 Set-up fee) you could have an identical Plan B which is simply Plan A without the set- up fee included "Premium 3 Months - No Set-Up" ($50/month).
To keep a single subscription plan and waive the set-up fee you could add an account credit for the amount of the set up fee amount. More info on applying credits can be found in our docs here: https://docs.recurly.com/docs/adjustments#section-issuing-credits Following this process would allow you to create a credit on the customers account that would be applied to their new subscription invoice and ultimately off set the set-up fee.
Alternatively you could create a fixed amount coupon to cover the cost of the set-up fee to be applied at the time of purchase. More information on fixed amount coupons can be found here: https://docs.recurly.com/docs/coupons#section-fixed-amount-discounts