http://en.wikipedia.org/wiki/Oak_Leaf_Cluster
http://en.wikipedia.org/wiki/V_device
I think an additional ribbon would be authorized then. I would build the rack on that other website to give you a visual representation.
From: EZRackbuilder.com in the army regulations section.
"If the number of authorized oak leaf clusters exceeds four and will not fit on a single ribbon, a second ribbon is authorized for wear. When the second ribbon is worn, it is placed after the first ribbon; the second ribbon counts as one award."