integrate amazon gift card on magento for specific users

I currently running a promo on my magento store (ver 1.7.0.2), which gives my customers $25 amazon gift card.

Currently it is a manual process where I sent the code via email. Instead I want to make it automatic via magento, as the user already having a login information for my magento website, they should login and redeem the offer.

I am searching for a extension which will provide me a popup which contains separate amazon gift code for separate users.