In that case, simply install a chunk of steel under the bicycle - 150kg or so should be sufficient.
I found steel rims to almost always work as long as you put it right over the middle line. In CA they often paint a little bike where you need to put it.
A simulated inductance circuit would do
Is there a way to visually tell what kind of sensor loop you're dealing with?
I can verify that a magnet makes the difference for my steel-framed e-bike, but really there's only half a dozen lights in town (Gilroy, CA) that I frequently use.
As far as I know all of the sensors that are embedded in the pavement use inductance.