The key lay in the back plate of one of my head torches, which happened to have several hooks and loops that you could pass a zip tie through.
Step 1: Materials needed
2. One or more Zip ties
3. A head torch with the right kind of back plate*
*My petzl was not suitable, what worked was a head torch I picked up in the local supermarket. They no longer stock them but when I wanted to make a helmet torch for my wife I found numerous cheap lights online which use exactly the same moulding for the back plate. In the end I got one like that pictured above from ebay for under £2 including postage if you search "head torch watt" you should find something similar.