Fenix has their
ALD-10 mount that fits their headlights, and has a GoPro interface that could be used to put the light underneath an out-front setup.
The light would be "upside down" with respect to where the buttons are, but I think that the beam pattern might work OK on their BC26R and BC21R V3.0.
The BC30 V2.0, in contrast, has a beam pattern that is not symmetrical up/down (plus, it's a fairly heavy light).