I use a strip of old inner tube with knot on one end. I cut a peice of minicell foam (because I have some) in the shape of the two fish lock block. The flash light is wrapped to the bar on the foam and the end of the tube is tucked under. Tip don't pull the tube to tight.

It does probably take a minute to put the light on the bar

It's cheap, soft and reliable and can be removed from the bar in a few seconds.