We commonly use a 3x12mm rare earth magnet (craft store, amazon, ebay...) that sticks to inside end of the pedal spindle to trip the GSC10 cadence sensor. It can also be glued, stuck with double stick mounting tape, or taped in place on the inside of the crank arm.
Agree that new accelerometer based magnet-less individual cadence and wheel sensors are very slick, but they're a lot more expensive than a magnet.