Is there a bike helmet mount available?
Fenix do make helmet mounts for many of their recent headlamps, but these are aimed at hardhats.
You will need to have a look at them and see if they will work for you on your helmet of choice. Please also check that the mount is compatible with the headlamp.
See Fenix headlamp helmet mounts ALG-03 and ALG-04.
There is also the ALD-08 which is designed to mount certain Fenix bike lights onto bike helmets.