.net expando objects in Matlab 2015b

Well, I got the expando object to create in Matlab 2015b , however, I have no idea how to add property/value pairs. I am looking to use this to marshal data from Matlab and pass it to a C# Dll I have written.

core = NET.addAssembly('System.Core')
x = System.Dynamic.ExpandoObject

>> methods(x)

Methods for class System.Dynamic.ExpandoObject:

Equals         ExpandoObject  GetHashCode    GetType        ToString