Have fun with your magnets, but fyi, I got a tip on a thread a few months ago. On the ground, you can usually find some seems cut into the pavement. Oftentimes, they are rectangles. I stop with my front crank over one of these seems, as Paul alludes to above, and shift the bike forward and backward, and it normally is enough to get a signal without dismounting or laying the bike down.

There's one other trick I found. I have a wireless odometer (CATEYE). I've noticed that when I'm near one of the inductor gizmos, my odometer will generate between 10 and 40 mph. This is my clue as to where I need to be.