Oh, true – I didn't address the obvious: click and hold doesn't work.
I messed up my own screenshot. I have it set to "and hold"... but it behaves just the same as just click. That's the first thing I tried, and... you know, maybe that's all I'm looking for – a way to make "click and hold" actually click and hold.
But if you click the yellow triangle, you'll see this Action Warning:
So it seems as if it needs another Action afterwards. I guess if I have to use a "Pause Until" action then I'd like it to "Pause Until" my device key is released. But unfortunately this option doesn't exist.
Hope I'm explaining this clearly? Thanks for any further ideas!