I am also looking for a way to do this. I play with a gamepad on my tv and scrolling in the menus does not work with the new UI inventory.
Plus, clicking that diamond and changing it back to Oblivion style doesn't stick. The next time I load a game, or sometimes just opening the inventory again, and it is back to the Nehrim style.
As a note, this is also the only reason I can't use the Darnified UI. I love that UI but it just doesn't work with a gamepad. I asked the author of Darnified a long time ago if he could fix it but he said he was too busy and pretty much cut it off there.