Nintendo promised some time ago the integration of the Nintendo eShop between both consoles and also the option to have access using different devices on the web, and looks like it’s possible right now, but quite limited.
First, you can now redeem your codes online thanks to this page, where if you’re logged into your Nintendo Network ID account, you will be able to redeem the game without being required to turn on your console, working right now with the North American and European regions.
Second, and this time only for the North American region, you can buy games online on the Nintendo Games site where you get a code to redeem which can be for you or a gift. For the moment it’s limited to Nintendo published titles. A few games like Captain Toad: Treasure Tracker and Super Smash Bros. for Nintendo Wii U can be pre-ordered, where the code will be sent on its release day.