Don't know if it's possible, but UI customization in Lr is very limited. When such questions come up, the stock answer is "look, it's the way it is for a reason..."
It could well be that if I had the option to move everything around to my heart's content, I'd eventually end up with the present layout because it's, well, the most efficient. But we'll never know, will we...
Backslash toggles before and after, if that's any help.
