Today, i forced the installation of Windows Phone 7.8 in one of my phones, the LG Optimus 7 (E900)!
I tried the Zune trick (WPCentral tutorial), disabling wifi/3g, etc… but nothing, no way.
I discovered SevenEighter, a very useful tool that force update to every phone! Very easy to use, and works very well!
This is my LG Optimus 7, E900 with last Windows Phone 8 update!