Crediting to Gift Certificate Balance Automatically

I'm looking to automatically apply 5% of a user's purchase to the gift certificate balance on their account, without them having to click a link to redeem via email. If I'm understanding how the system works, would I simply need to UPDATE/INSERT into zen_coupon_gv_customer (5% of zen_orders.order_total) for it to appear in their account?

I'll be creating a separate table to track whether the credit has been applied to the order so that it isn't applied multiple times.

I've gone ahead and done the above - site seems to be working fine, people are able to see their balance, it adds correctly if there's an existing or creates an entry for the customers' id if there isn't one.

Would still appreciate some feedback from anyone familiar with modifying the giftcards/giftcertificates - to see whether I'm missing any steps or if there are bugs I should know about.