To get the latest version of Android on your Nexus device without having to wait for the Over-the-Air (OTA) update, follow these steps:

But first of all: There is no warranty and I am not responsible for actions you make! I updated to Android 7 (Nougat) without any issue.

1. Update or install the latest “Android SDK”. You can find the latest sdk on developer.android.com
2. Be sure to have the Google USB Drivers installed and your device is recognised as a nexus device. To verrify that navigate with your shell to the “android-sdk/platform-tools” folder and enter “adb devices”. You should see at least one device with an ID and the name “device” beside the ID.
3. Get your OTA file from androidpolice.com (or somewhere else)
4. Rename the file to e.g. “nougat.zip” and move it to your “android-sdk/platform-tools” folder.
5. Run “adb reboot bootloader”
6. Press the “Volume up” button until “Recovery mode” appears, then press the “Power” button to select this.
7. A warning sign appears with a notice “No command”. Just hold the “Power” button and press “Volume up” to enter the menu.
8. Now select “Apply update from ADB” (volume up/down to navigate, power to select).
9. Run “adb sideload nougat.zip”. This might take up to 10 minutes.
10. After your nougat.zip is successfully loaded and installed on the device, select “Reboot system now”. This action will prepare your apps while booting. It may take some time, depending on how many apps you have installed.

Have fun with the new version of Android :)