[rodneym]

I have a different camera system that uses a remote lipstick camera, mic and hdd.
I mounted the camera with velcro right under the sun visor. This gave a really good driver's perspective and of course I placed the mic in the passenger footwell, with the mic impedence set on the highest level.
Sponges may be a bit thick but I would suggest an open cell foam like used for windscreens on mics. Also, experiment with different types of tape over the mic holes.
What you will not end up with is a high quality signal to noise ratio, at least in a Cobra.