"the billy book case CD insert is a good idea in principle but has at least 3 drawbacks:
- the standard fixing method is not very solid,
- it puts the front face of the insert in line with the front of the bookcase, which looks bad,
- and to add to the bad looks it leaves a small but noticable gap between the top of the insert and the shelf above.
make two "L" shaped inserts from the packing pieces and two brackets. any small brackets will do, i used surplus billy wall anchors. these will be used to space the insert from the back of the book case.
replace the inserts and slide the shelf / insert combo in in front of them. voila!