Yep the torch is for the helmet. I am going to try the lockblock, but if that doesn't work I am going to use some velcro tape.
At the moment I use one of these:
http://www.dealextreme.com/details.dx/sku.14909
and it is exactly the right size to fit in the central vent of my Giro Hex, and can be held in place with an elastic band (in a loop, so one end over the front of the torch, then stretched over the top of the helmet, and then the other end goes over the back of the torch)
However as its now older technology I thought I would try the 900-lumen version. However I am now thinking that, that torch might be too bright.