Gift of $25 towards any purchase - How to do it?

Hello all,

So, our marketing is looking at creating an offer that has to be redeemable online as well as over the phone that is you get to use $25 Gift Cert as a gift from our organization towards any show for our current/next season.

Now we can't do negative fee cause they don't exist.

We can create the "gift certs" in Tessitura by creating them in these patrons accounts and paying them off with a "dummy payment type" that we would create just for this.  However, the issue will be when they patron uses the gift cert that money would then hit the shows that the patron purchases with. This in all the reporting would create an overstatement on the show. We can't going to all of the reports canned and custom to "ignore" these gift certs and the money that's attached to them.

Promo codes won't work either because we don't know how many tickets they will purchase and depending on that there would be an unforeseeable number of price types needed to find the combo that would give the "$25 off". 

Now, of course - I've been charged with finding a way to make this happen.

Does anyone have any thoughts or ideas? Is there something I'm not thinking through?

Thanks in advance.

JEFF