http://www.instructables.com/ex/i/E7...E506/?ALLSTEPS

Check the link for photos.
Most likely illegal, I would think.

Intro Traffic Light Trigger for your Bike

Not feeling ferrrous enough to trip the induction loops that trigger green lights? No problem - just epoxy a rare earth magnet to your shoe! Inspired by a product marketed to motorcyclists, which is basically a big neodymium magnet to stick under your ride. I thought it might be better to get a slightly smaller magnet closer to the road.
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Step 1 Dremel as needed between the lugs of one heel

I always put my right foot down, so I ground out a little extra space on my right heel. Luckily, my Sidis have tall, widely-spaced lugs, so I didn't have to remove much material.

Step 2 Epoxy the magnet, backed with a washer, to the shoe

I used PC-7 heavy-duty epoxy paste and coated the entire magnet, both to protect it and to stick it firmly to the heel. Backing the magnet with a washer helps to focus the magnet field, aiming it down (and not up into your heel, not that it should do anything to you anyhow).

Step 3 Using the magnet to trigger lights

Look for the round or diamond-shaped cuts in the asphalt that show where induction loops are buried at intersections, and set your heel down near the tar lines. Here in Portland, some lights helpfully have a small bike between two hashmarks which you're supposed to line your wheels up with, which is a the perfect spot (and more sensitive, too).