I've been trying to come up with a system to mount a SF to my helmet, a Bell Venture, as well. Your helmet looks somewhat similar to mine.
One option that I've almost gotten around to is to take a short, small diameter piece of PVC and glue it to the top of the shell at the very back where it is almost flat. It would be a stubby little vertical post atop the very back of my helmet. I found a "reducing connector" at the hardware store and cut in half in order to use the smaller diameter section. The SF seatstay mount would then be clamped to that and it would allow the light, when mounted, to overhang the back of the helmet. Depending on how far the light is from the edge of the shell, it would be adjustable to some degree.
My only issue has been deciding on glue to use and sanding the base of the PVC piece so it fits the slight double bevel of that part of the helmet's shell. I would also like to figure out a retention system so that if the mount were to fail, I wouldn't lose the light. Probably a zip tie threaded somewhere. As I'm not riding at night much now, the project is on hiatus.
I actually just now found the
BLT Wazoo DX helmet light mount available separately. I had found the light before and the mount caught my eye but I didn't want to buy another light just for the mount. It looks very similar to the mount used for the PBSF. The seatpost mount for the non-helmet Wazoo DX looks almost identical to Planet Bike's. If it's compatible, it's just a matter of fitting that velcro strap to your helmet.