Thanks Brad, but I already bought it through Amazon a couple of days ago.
Now, to those who have the same dilemma, I highly recommend avoiding the Amazon store like the plague. Buying the gift card was the easy part, but then I discovered that my brother doesn't have an Amazon account. No problem, right? Wrong. To make things easy for him and still have any semblance of this being a gift, I decided to do the registration for him. Unfortunately this required many more steps than I remembered and providing a lot of mandatory information than I wanted to share (including a credit card number). Eventually I ended up in a situation where I finished registering and had the application bought, but since I did it through website rather than the AppStore (like I frequently do with Google Play), the program didn't show up as available for download. The result was that the gift card was consumed, but the AppStore still showed a [$7.99] button as if I didn't purchase the software. It took me a long time to figure out that if I click this button it doesn't purchase again. At this stage I still had my credit card linked to my brother's new Amazon account, so I unlinked the card and decided it's safe enough to click this button. After clicking, the button changed to [Download] and I was able to get the software and install it. But all in all it was a really bad user experience.
I should have just temporarily linked my credit card to my brother's Google account and purchase it this way. Far less steps, and my brother (who doesn't own or plan to own a Kindle) wouldn't need to install another AppStore just to get a single application to run. Live and learn.