Oculus Overlay is a program that can warp in realtime any source content of any size from any desktop window into the Oculus Rift format. It is necessary for getting a lot of things working with the Oculus Rift, but consider it a last resort.
Setup for Oculus Overlay is pretty straightforward to get it working properly. Once you load up the program then you can just press Z to fullscreen it to the Rift.
Setup for the DK2 is a bit more complicated than the DK1. Currently, the program technically supports just the DK1, but can be made to use the DK2. To do this, follow these steps.
Step 1 Edit
Load up Oculus Overlay. Once it's up, you'll need to change the screen resolution of the DK2 to let Oculus Overlay *think* it's the DK1. Change the DK2's resolution to 1200x800.
Step 2 Edit
Once you've changed the resolution, go back to Oculus Overlay, and press Z. This should fullscreen Oculus Overlay onto the DK2. But, we want the full resolution of the DK2. Next, what you need to do is change the resolution of the DK2 back to 1920x1080 with Oculus Overlay still fullscreened. When this is done, Oculus Overlay will still be fullscreen, but now in 1080p! Huzzah!
Once you've set up Oculus Overlay, you'll need to configure it further to fit your view. Luckily the program is incredibly versatile, so changing the settings to your liking is easy. If you press space, you'll see a menu that will show you all the commands that you can use to change the view to your liking. I recommend making sure it fills up your view, and you'll need to adjust it for the barrel distortion as well.