You're probably right, but you haven't seen my lack of talent at welding
I was considering a slightly different tack. If I made a thin disc with a small slot in it that sat flush with the cam wheel, and the slot lined up with a hole in the JP wheel, then this would be more or less equivalent to the OEM solution, and would be easy to keep in balance. It doesn't matter if it's a tooth or a space to the ECU, as long as the sensor reads a change of state.
The only snag is how best to attach the disc to the wheel, since if it sits in the recess, it won't be keyed and I'm not completely convinced there's enough space to fit a disc of sufficient diameter outboard of the cam wheel.. Back to welding again...