How do I get custom properties of a class with TypeDescriptor.GetProperties()

I'm trying to retrieve custom properties of a class that inherits ICustomTypeProvider, that have custom properties created during run time similar to what is described here: http://ift.tt/1Sc2TtD

If I use TypeDescriptor.GetProperties(myObject, false) only the properties defined at design time are returned. How do I retrieve any custom properties that object may have if it inherits from ICustomTypeProvider?