A couple of ideas for mounting flashlight to helmet on a more temporary and less Fred-ish basis:
1) the Fenix website sells bike/helmet mounts called bikeblocks and lockblocks, which use a u-shaped mounting for the flashlight and velcro to secure to a bar or helmet. Depending on the design of your helmet one or the other should work.
2) you might try using a large rubber band or perhaps hair crunchy and use it to mount the light in much the same way as a Dinotte headlight is secured to handlebars using an O-ring.