Trigger a Script based on a coupon use, and / or dissalow other coupon usage?

27 0 1

Hey all, 

So I've managed to get a "buy 1 get 1 half off" script working on my Dev site, but it's applying it to all orders without a coupon code at the moment. (I realize that's how it's designed)

but, ...

I'm trying to find out if I can create a 0% coupon to trigger the script to only run when that's entered?  That would prevent customers from using a different coupon and provide me a decent way to track the usage yes?