Discount code combined with free shipping

[relentlessrebel]

Hello, I have free shipping on orders over $99.  I have this set in my shipping profile.  I also have discount codes on my site.  I can check for a % off discount code to not combine with other codes or a shipping code.  But, what I'm trying to do is not have my discount code and free shipping combine (or be stackable).  I'd like for someone who orders over $99 to decide if they want the free shipping or if they want to use the discount code.  How can I do this? I'd like it to auto populate free shipping on orders over $99, but I'd like the free shipping to go away if they choose to use a discount code. Any ideas?