Well, I've seen one or two advertised in various crew rooms and on the internet, but after looking at pictures of them, I decided to do it myself. I took some crude measurements (basically some marks on a sheet of paper one day at work), then went to the local hardware store and bought a sheet of aluminum, about 18x6 inches (for about 3 or 4 bucks I think). Drew some lines with a marker, cut it down with a good pair of scissors (careful for the metal shavings), held it to the edge of the kitchen counter and made some 90 degree bends with a hard-cover book. Covered the sharp edges with electrical tape. That was version one. I tried it out for a few trips and decided to improve it. I took a second piece of aluminum (actually, it was left over from the first cutting) and added to rearward "slant" to it, so the center of my binder was resting underneath the center of the bottom edge. The first version had an edge that kept catching my right hand whenever I was reaching for something on that side. So now I have a pretty workable holder device. I usually slide the clipboard almost all the way up to the side window handle, and then clip my holder under the clip, and it slides neatly underneath the plactic window frame. I don't know if my version would be strong enough to hold a large Jepp binder, but I usually keep only the Jepps I need for any given month in a smaller Jepp binder, and it works great. I usually clip the edge of my binder underneath the clipboard clip for takeoffs and landings, but for normal flight, it's fine just sitting there. It kinda blocks access to some of the storage areas and the cupholder a little, but it still works at night to move the overhead light over (the top of the light usually stops at right about the top of the page), and it's still better than setting your binder on top of the storage areas or worse, behind your shoulder on top of your bag. I don't think it would work on the left side, with the tiller and all, but it works on the FO's side pretty well for now.
Kinda long winded explanation, but give it shot.