I used a small bit of helicopter tape to affix a rare earth magnet to the chainstay, then simply put more magnets on top of the first one until you have them close enough to trip the Reed switch.
@Dammit started
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I used a small bit of helicopter tape to affix a rare earth magnet to the chainstay, then simply put more magnets on top of the first one until you have them close enough to trip the Reed switch.