They tend to be designed by the "bar of soap" school of ergonomics and have no real surfaces to key onto. You might try a long (diagonal) section of inner tube used as an elastic band. Put it over the front of the flashlight, under the bar then on top of the rear. Ive done this with an AAA maglite on a hire bike, coming back from the pub at night.
Wind-up LEDs are a good idea for long expeditions, emergency/survival use. They dont illuminate much in pitch black but are better than dead batteries.