I just thought I'd let you know how I mounted an L2D to my helmet - in a really secure, removeable and user friendly way! I had to sacrifice a bottle mini-pump mount, but I think it is worth it.
I used a mount from a topeak pocket rocket mini pump, which I can only assume is also available in the US:
This mount fits an L2D PERFECTLY in it's holder side. It uses a rubber O ring to securely hold the pump, which is perfect for removing the torch when not required. With some cable ties, I found a suitable place on my Giro Monza to attach it to- I imagine that other helmets would also have equally suitable places.
Here are some photos:
Once secured with cable ties it is very stable on the helmet with very little movement. Used with P7s on the handlebars it is a fantastic combination for speedy night time road riding :-)