Is there some way to trigger adding a specific product to an open cart?

[DrByte]

Do you know if anyone ever pushed that tutorial example far enough to know it will work?

I know I did, years ago. Not sure if I still have that code around anyplace.
It's very challenging to also have an Admin interface to manage all the possible options. What I'd done was all handled in a PHP file, without any admin-side controls about what products qualified with other products etc. Very rigid implementation. But certainly doable. If you want nice admin controls and switches and fancy dialogs you'll be needing to invest more to provide that.