I'd love to find a way to do this as well. For me the "Desktop Peek" function is useless and ctrl-space is used in a game that I play.
The only solutions that I could find that might work (haven't tried either) were to disable all the win+ hotkeys or to use AutoHotKey to clear the win+space hotkey.
Would it be possible to allow FARR to hijack or override an already taken hotkey?