Maybe it's a well-known trick... but I paused... rewound... did some searching, scratched my head, and then the "ahhhhh.. I see" sunk in.
I think I know the trick you're talking about. Sometimes I will either extrude or duplicate a vertex and move it to where I want to snap the 3D cursor. It's the most precise method I've found for snapping the cursor exactly where I want it to be, in this case for establishing origin location. While we can't select the 3d cursor as if it were an object we can place it wherever we want with our mouse. Sometimes that's good enough but in this situation I needed it to be precisely placed. That requires an extra step or two.
I personally don't know of a less convoluted way to do it. As you continue learning computer graphics and Blender, you'll find that there's always several ways to skin a cat. If you can find a better way to do it, do it! Then share with us :)