Update: Files have been updated to make the app more stable and reliable and indeed it does work better now. (5PM ET)
Windows Phone Hacker has released a new “wrapper” tool called 'Seven-Eighter' that reportedly makes manually installing the 7.8 update less cumbersome than downloading all the files yourself. The app comes in x86 and x64 and is a simple executable that you run on your PC (you’ll need to give it permission in Windows 8).
In theory, it’s the same method we detailed in our CAB file post yesterday---you specify the languages on your device and then it fetches the files for you, all through a progress-bar UI.
Since Windows Phone OS updates are cumulative but iterative in the process, you’ll have to go up through Tango before proceeding to 7.8 meaning there will be a few cycles of updates.