This creates a directory called /ALL , finds all of the files ending in .mov in the subdirectories of the current folder, and then puts symlinks (which are links to the movs that act like the files themselves) in the folder /ALL
This ALL folder can be added as a watch folder in Media Encoder. Works great
Symlinks are location based so if the original media is moved they will stop working. If more media is added to the original folder the command can be run again (though wouldn't recommend doing this during a copy) and the new files will be added to ALL - and will be picked up by the Media Encoder watch folder.
I didn't realise that Media Encoder's watch folder moves source files into a "source" folder when complete.
This meant all of my rushes have been moved out of their original Alexa file structure and into All/Source
With Alexa rushes following a fairly simple naming structure it was reasonably easy to put them back into the right place afterwards - but be aware of this (which partially defeats the purpose of the original solution)