I was trying to think up ways to use
this mount from DealExtreme. A family member actually came up with the best idea--to combine it with one of the Planet Bike mounts.
The 25mm clamp fits my UltraFire 18650 flashlights like a glove. Unfortunately, this is my rear, red light, so this mounting is better used only if you can clamp it around your seat post or are using it with a white light as a front light.
If you look closely, you'll see the plate under the thumb screw is not stock. It was made to clamp on to a picatinny rail that's larger than the width of the Planet Bike mount. So, I made a custom plate that reduces the clamped width to solve the problem. Also, you may be thinking, "What's stopping it from sliding right off?" Well, the bolt that the thumb nut tightens down on is not flush with the bottom of the flashlight mount. I used a round file to carve a channel into the top of the PB mount to clear the bolt and prevent the mount from sliding fore/aft. Finally, I put some rubber on either side of the bolt to prevent the flashlight from rocking when attached, as a slight air gap would be present otherwise.
It took a bit of work, and the custom plate is not something I want to mass produce, so I've ordered some other flashlight/laser mounts for guns that have a narrower clamp on the base. I'll report back on how well it works.
Edit: Oh, and of course you can easily reverse the mount, either by removing the top plate on the flashlight clamp, or taking a much quicker route and separating the flashlight clamp from the planet bike clamp by simply unscrewing the thumb nut. This also makes it easy to remove the flashlight itself while still leaving the planet bike mount on the bike (and the clamp still on the flashlight).