I just picked up a Cateye TL-LD1100 for my commuter and want to move my PB Superflash to my helmet. I've found two spots on the back of my Bell helmet that look like they could work - one upper position that I created by looping 4 zip ties through a couple of vent holes:
and a lower position that I get by attaching to the rear tension strap:
Both seem to work, but the high position seems to angle a bit upwards, and the tension strap angles a bit down. Here's an example of the upper mounting position from the side:
Is there a better solution that any of your are using that might provide some more flexible options with regard to height and angle? Is this less of a concern as this is an secondary rear light?