Two ideas. First,just look around. I've seen dozens of pedal reflectors laying on the ground. Pick up a couple and RTV them and they should stay put. Second,just put some reflective tape on the pedals. Nothing to fall off.
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C'dale BBU('05 and '09)/Super Six/Hooligan8and 3,Kona Dew Deluxe,Novara Buzz/Safari,Surly Big Dummy,Marin Pt Reyes,Giant Defy 1,Schwinn DBX SuperSport,Brompton S6L/S2E-X/M6L-X/S12 T Line