flat shipping cost coupon

I'm trying to create a shipping coupon, and not having much luck. first i am using PRO, and the normal coupons seem to be working fine.

what i would really like to do is offer a coupon to my customer for say 3.99 shipping today on any order.
if they enter a promo code they only pay 3.99 for shipping.
any ideas?

thanks,
JIM

If it is for a specific shipping that always comes out to a fixed amount, example 10.99, you could put in an amount coupon that would take off 7.99 for that specific shipping, as long as it is one of the supported shippers. What shipping module are you using? Also is it a fixed rate?

UPS, and it isn't a fixed rate. we use the ups module in virtuemart.