Welcome, Robert (not another!) to the OEM forum.
Why not just shell out for a plain reed switch? That’s what I’ve got, wired into an emonTH (but it’s the same input circuit). I needed a capacitor to take out the contact bounce, but the de-bounce software in the emonPi2 should not have a problem with a reed switch.
You do indeed wire it between the pulse input and GND, and use the built-in pull-up.
Check the Docs: Other sensors — OpenEnergyMonitor 0.0.1 documentation for the solder links.
The bare reed switch (no case) is just visible end-on sitting in a groove in the (black) piece of wood. Two screws are terminals, the third upper one secures it all to the meter, which conveniently provided a mounting cut-out ready to accept a switch.
That switch was £0.85 (plus carriage) at the time.
