free shipping coupon allows upgraded shiping to be free

Hi!

So I have my shipping set up with zones, and I have it copied 3 times to offer different types of shipping:

USPS 1st Class,
USPS Priority
USPS Express

Those modules are working great, it offers the correct price whether they are in the US (where I am) or international.

So, my problem is when I offer a free shipping coupon, I want it to only give free 1st class shipping -- not free upgraded shipping. Someone used it for free Priority shipping this week, and I'm guessing they could have just as easily used it for Express.

Any ideas on how I can get a free shipping coupon to only offer free 1st class shipping?

thanks so much,
Amy

Bumping to see if anyone has any ideas for me..

Seems new code is necessary. This rather complex thread might have an answer:

http://www.zen-cart.com/forum/showthread.php?t=75489

Thanks so much, I will check it out.