Brian,

The way I ended up doing it on my CD cases and it works fine, is to
take some of the long metal shelf standards
I routed a dado down the length of each shelf and installed the
standard so that it was level with the rest of the shelf. Since
everything is black, it's difficult to see if you're not looking for
it and once the shelf is full, it's completely invisible. I made a
wooden end piece with a flat metal post underneath that fits into the
track and you can move it along the holes as you get more CDs. When
you fill the shelf, remove the end and move it down to the next shelf
to continue filling.

I had thought of something similar also, though with a different type of
shelf standard. In fact, I already have a few shelf standards I bought
years ago for a project and then never used them. So this may be a good
place to put them to use. I'll keep it in mind. Thanks!

Anthony