Use what you've got?
Mount the light on the underside of the handlebar. I have mounted several of my lights under the handlebars over the years.
... They tend to be much more stable position wise, 'hanging' from the bars (much less 'wandering' up and down on rough stretches).

...On cheaper (Magic shine clones) headlights the area where the power leads enter the light head is not really sealed for upside-down position in the wet. Easily remedied with some 'poster putty' and 60 seconds of time.