So you're trying to get it look similar to this picture ?
Trottimus uses a little cheat here I think and have left 2x2 slots in the middle (that are over autoattack button) vacant.
As you can see from the smaller setup above there's 5 slots each side (10 total) of autoattackbutton but in reality there's always 12 buttons in 1 bar. This means the 2 slots in the middle are simply not used.
I know it sucks that we have to do tricks like these but we are left a little choice here because the skinning is so restricted in lotro.
If this doesn't answer your question I hope Trottimus himself will try to guide you as he knows his skin better.
If you have problems with my UI I might be a bit more of use