WPF: Implicit Infragistics Ribbon Styling using BasedOn

Question

Hello, I'm using the WPF infragistics ribbon and I'm trying to work off their styles using the BasedOn attribute. This work well when the x:Key is defined however in the case where I want to override the property on a border located inside an implicit style, what's the best way to do that without duplicating the entire style into my customStyle.xaml?

Thanks for the help.