how to define this dictionary in silverlight 4 XAML

Question

I want to Define Dictionry with the following XAML


Dictionary<Tuple<ModifierKeys, Key>, ICommand> I know I need to create class that inherit IDitionary , byt how to call it or use it withtin the XAML
on the level of the usercontrol , I want to creat shortcutlist , to pass to global behavior that catch keydown in MVVM model , so I want to pass this dictionary to the Behavior to check against