I have had some hack at Oxygen style. This all was for allowing Oxygen draw custom categories at KListView. My proposal is this one:
Of course, here you can find the patches for kdelibs, and for oxygen style.
I removed some hard coded values that had the previous version and that were just for testing reasons. I still need to handle properly the sizeFromContents method.
If you have any comments or suggestions feel free to contact me.