WPF Binding Expression Alternatives
Via this post from WiredPrairie blog.
The post holds links that explain approaches for extending the binding extensions.
Extending "Binding" or "BindingBase" is pretty tacky, this is due to the fact that BindingBase.ProvideValue is sealed.
The posts illustrate an elegant approach for wrapping it up and creating your own MarkUp extension to provide you with the functionality you desire.