On a more serious note, if you pay attention to the lines that are often cut into the pavement to install the detection wires, you can position yourself to increase your chances of being detected. If it is a rectangular cut out, don't put yourself in the center. Instead position the bike right on one of the parallel lines so both tires are on the line. Get as much of your bike over the wires as possible. If it's been paved over since initial install, you'll have to experiment on where to position the bike. Sometimes the middle of the lane is best if two adjacent rectangular sensors are installed per lane.
If that doesn't work, you can try turning off the motorcycle and then starting the engine. This causes the electric starter motor to spin up which should trip the magnetic field sensor beneath you.
Finally yea, the magnet thing could work. But I suspect you'll need really powerful magnets. Neodymium is good, and often found in hard drives. But modern hard drives use increasingly smaller magnets. So you're probably better off finding some on ebay for cheap. Should probably be strong enough that you need to handle them with respect: AKA they could pinch your fingers or slam together if you aren't careful. I have old hard drive magnets that will cling to either side of my wrist for example.
Of course, if it continues to be a problem, report the intersection so someone will look into the issue.
As a last and very illegal resort, you may have noticed a small device that often sits on the top of traffic lights at major intersections. This is a sensor on emergency vehicles that is calibrated to turn the light green when it reads a strobe light at a specific frequency. If you figured out the frequency and mounted a strobe light to your motorcycle, green lights will appear as if you were an emergency vehicle! Yay!
Edit: Looks like some of these strobes use infrared so you can't even see the operator triggering the green light...Interesting..but still very illegal heh heh