It's more fun to do things in software than hardware. Inspired by this, I had some luck removing star trails from unguided photography. I may post more detailed instructions later. You need to install ImageJ and the DeconvolutionLab plugin.
Here is what I did with Lyra.
Step 1 is to rotate the image, e.g., in Gimp or Photoshop, until the trails are all horizontal.
While doing this, identify the length of the tracks in pixels, in this case 20. Create an all-white 20x1 image. (I used ImageMagick, but a photo editor can also do it.) This image is the point spread function. Then run ImageJ. Then load both the 20x1 image and the rotated sky image. I made sure the sky image was the active image in ImageJ (click on it), and ran Plugins | DecompositionLab. Set the algorithm to Richardson-Lucy. In the Background module, set Subtract Background and Use minimal intensity to darken the sky. Run and here it is:
It's far from perfect but much better. Here's a before-and-after zoom. Note how nicely the double star was picked up.
I took my Panasonic DMC-G1 camera, set it on the widest setting, focused on something lit up in the distance, set it on manual, maximal aperture, 14mm setting on the 14-45mm lens, 30 second exposure, and put it upside down a table on our balcony. I was surprised how much more you see than with the naked eye. Here's the result (with the slightest bit of editing to crop and to darken the sky).
That's Lyra at the bottom and Hercules in the middle. If you look really closely, you should be able to see M13:
At 30 seconds, even at this low, low magnification, star trails start.