I have fairly strong fingers and it's a big 4.5mm clock key, so I don't have much leverage problem. If I did I'd simply screw a couple of strips of wood over the metal key handle.

Okay, mine is one of the most primitive autoharps you can get, and I mainly use it as an exercise in harmonic austerity, but it does stay well in tune.

Unless the Korg does meantone tuning, isn't it always going to be worse than a pitchpipe? Who wants an equally tempered autoharp?