Google Play's web store will sell you Google Play credits
Purchase Google Play credit directly from the website
All you need to do is to go do the full Google Play website and scroll to the bottom. You will find on the footer, an option entitled "Buy Google Play credit". Click on it and it takes you through a fairly easy checkout process. Then, when you're tired and worn out after along hard day, a new game or a premium app is already paid for. And yes, you really aren't saving any time overall, but that's our little secret.