> GUI would probably be easy but CLI may be tricky
hmm.. I was thinking the opposite actually. Also, a CLI option would work in either case, whereas a GUI option would require a CLI option for --no-gui users. I would again suggest we survey what other programs do to get a feel for what options have been tried before and if there are methods we do/don't like. We aren't the first to play this game.
And triggering on something like the 'error: unknown function...' might work, but will require learning how the error handlers are currently called.