WHMCS: Exempt Setup Fee from Promotions

Hello, We are using WHMCS and run some promotions which use PROMO codes. The issue is that WHMCS promo codes will apply to the sub total. There is no way to exempt the setup fee. For example: Package = $50 Setup = $60 Subtotal = $110 Promo @ 100% will give $100 off. We need it to be only $50 off and not have any effect over setup costs. Bid away!