I have nice news, as i read in the What’s New in WPF Version 4 page in MSDN, data binding to InputBindings is now fully supported in WPF4.
Bind to commands on InputBinding
You can bind the Command property of an InputBinding class to an instance that is defined in code. The following properties are dependency properties, so that they can be targets of bindings:
The InputBinding, MouseBinding, and KeyBinding classes receive data context from the owning FrameworkElement.
Update for post: CommandProxy: Howto databind a ICommand to an InputBinding