[ic] Shipping calcs with gift certificates

[Bob Puff at NLE]

Hi gang,

I've got a cart that uses gift certificates (called Donations).  The shipping formula is based on 
the total amount of the order, not by weight.  ($1-$50 is $5, $51-$100 is $10, etc..)

The problem is the customer doesn't want the donation amount (gift certificate) to add in to the 
formula used to calculate shipping.  So if the cart has $100 of product and $50 of gift certificate, 
they want the shipping formula to reflect the amount based on $100.

Would this require some perl in the catalog.cfg, or where (and what) would this entail?

Bob