AbleCommerce Shopping Cart Software

I'm working on code that hides free shipping methods based on a net order amount, not the total of the products. Basically total of products less discounts and coupons to come up with the minimum order amount to qualify for free shipping. I'm fighting the one page checkout because the coupon box doesn't show until the shipping methods also show, then the page doesn't refresh to pick up the new order amount after coupons are applied. I can try to rebind the shipping methods, but it might be easier to have the coupon box visible until customer selects to use billing address or another shipping address. Is there a definite reason that the coupon box isn't visible on first going to one page checkout? Is there a better way to refresh the shipping method selections?
Thanks