Promotion Excluding Shipping


I'm so sorry if this has already been posted some place, but I'm trying to set up a promotion ( coupon code ) that is calculated before shipping is added - we need the customer to pay for shipping. Another thing we need is to allow the customer to use the coupon even if the order subtotal is below the coupon amount. Example: the coupon is for $50 but the customer is only ordering something for $10 - we need the $10 item to be discounted but still charge the $8 ( or whatever ) shipping. Will the remainder of the coupon be recorded in their account? Is this possible? I've tried what I think is every combination but can't get it to work. If anyone can point me in the right direction I've really appreciate it. I've looked at this so long my brain is just spinning in circles.