I couldn't get Scratch to work direct from a network share, so I used a method similar to @FudgeyBear, and used a script to copy the files onto the local drive, seems to work fine.

1, Download Scratch

2, Unzip the .exe file

3, From the $PLUGINSDIR, unzip the app-32.7z file

4, Copy the contents of the app-32 file into a shared network folder

5, Create a script

Robocopy /copyall /s /e "\\SERVER\NETWORKSHARE\Scratch3.6" "C:\Program Files\Scratch3.6"

6, Create a GPO to create the folder Scratch3.6 in C:\Program Files\

7, Create a GPO and assign the start up script created in step 5

That should do the trick!