The title says the request. Feel free to ask questions if you need me to clarify anything.
This is unfortunately not something an extension is able to do. Extensions use the SketchUp API to interact with SketchUp’s model and entities, not the operating system APIs to interact with hardware.
And – sorry to say that – it is also something not in the scope of what an extension in a specific app should do (in my opinion). From a software design perspective it makes a lot more sense to configure hardware and input devices at a higher level. You can consult your touchpad settings or synaptics manual to enable 3-finger tap if it is not yet enabled.
Since trackpads are relative input devices (in contrast to touchscreens), they use different interaction sequences so that the absolute position of the event is defined. Most trackpads use tap (finger down and release to define the drag start) followed by finger down and move to emulate dragging.
This works the same way for three finger tap + release + drag to orbit in SketchUp.
So Ruby doesn’t have an input option for trackpad gestures? In hindsight, that kinda makes sense. Unfortunately, my computer doesn’t have a gesture for clicking the scroll wheel that I can find. Sometimes a mouse isn’t an option if I’m not using a desk.