How to expose a custom collection through the MAF pipeline

I am using the Managed Addin Framework on .Net 4.5 to help handle scripting on my host application's objects. We have custom collections defined on the host application that inherit from CollectionBase which contain a list of custom objects and provide additional functionality.

Is there a way to define the pipeline in such a way that the custom collection can be iterated within an AddIn by using "foreach" and also have that pointer supply access to the custom methods defined on the custom collection?

For example, the AddIn code should be able to do both of the following: 
... = HostObject.CustomCollection.getStuff("somecriteria");
and
foreach(CustomObject co in HostObject.CustomCollection) ...

I know how to get the collection across the pipeline allowing "foreach" iteration but that requires me to have a separate interface to the custom collection if I want access to the custom collection methods. Any thoughts?

BR,
Saminteger