How to query default property of custom class for DisplayMember and ValueMember

Question

I have this class (extremely simplified):

Class MyClass
    Default Public ReadOnly Property Item(ByVal key As String) As Object
        Get
            Return key
        End Get
    End Property

    Public Overrides Function ToString() As String
        Return "ToString"
    End Function
End Class

I'm setting an array of those objects as datasource to a ComboBox. I'm setting ComboBox DisplayMember and ValueMember to expressions that should return meaningful objects when passed as key parameter to ClassEx.Item default property. But this is ignored and ComboBox displays what is return by overridden ToString function.

How can I force ComboBox retrieve values from Default Item Propery passing DisplayMember and ValueMember settings as parameter (as it does, for instance, with a DataRowView?).

Thank you very much