Arnold Vink has made a custom Windows Phone 8 SDK Tools Lite pack which includes just the tools you need to developer unlock and sideload the application on your Phone from Windows 7 and Windows 8.
FOLLOW THE INSTRUCTIONS
1) Download: Wp8 SDK 8.1 Lite … (65 MB)
2) Extract the zip file and run InstallWP8SDKToolsLite.bat to start the installation!*
3) After a few minutes WP8 Lite SDK should be installed on Windows 7 and Windows 8
4) Make sure you have an active (Free) Windows Phone Developer account registered
If you receive any errors do follow these below tips
* If a “Connectivity.dll” error shows up during the SDK installation make sure to install .NET Framework 4.5.1 before running the SDK installation which can be downloaded here: Microsoft Download Center … x?id=40779 (66 MB)
** If an “IpOverUsbSvc” error shows up in one of the tools and you have already tried rebooting your PC, try reinstalling your Phones drivers by switching it to an other USB port and make sure Windows Update downloads the drivers.