[Flippant]

an expansion of nicole's sunglasses idea:
you will need:
1. a lens from an inexpensive pair of polarized sunglasses
2. 2 rubber bands
3. scissors
4. your existing lens hood

You can make a slightly less awkward version of the 'hold a pair of sunglasses in front your camera' trick by using some rubber bands and the hood that you normally use to block the sun. Using rubber bands (1 has been cut, and tied on the polarized lens) as shown, attach the lens to the reverse end of the hood so that when you clip on the hood in 'stowed' (reversed) position, the rubber bands hold the polarized lens up against the camera lens. this way, you can unclip the hood/filter, adjust the zoom, and clip back on the hood/filter easily. just keep the filter/rubber bands in your camera bag and whip out when needed.