How to setup Windsor component that needs to depend on a dynamic string?-Collection of common programming errors

I have a Castle Windsor component, that depends on a string. The string needs to be determined at runtime, based on another string, which is constant and can be set in the component configuration. How do I wire this up using Castle Windsor ?

The problem is general, but the specific scenario I need it for is a class that takes the full path to file in a constructor, but since I am running a ASP .NET app, I only know the virtual (relative) path of the file when writing the configuration file.