(Here is a link to some useful videos on dependency injection and Castle Windsor that helped me to understand why they are used).
Part of the framework uses a class called WindsorContainerBootstrapper which calls a GetInstallers method which looks through all referenced assemblies and finds and returns a list of the Windsor Installers that are contained within them.
This was designed for console applications though. To make this work, I made a change so that it uses the HttpRuntime.BinDirectory method to correctly locate the bin folder where the assemblies are stored in a web application.
This extra class could not be added to Endjin.Core.Composition though as HttpRuntime is dependent on System.Web, and Endjin.Core.Composition uses the .NET 4 Client Profile which does not support this.
So I added a new WindsorContainerWebBootstrapper class to the project and called it in the dependency injection configuration to initialise a new Windsor Container.
This means I can now resolve my types dynamically.