Dim designerHost As IDesignerHost = Me.GetService(GetType(IDesignerHost))

When creating a subclass overrule the abstract PerformLoad function to load the workflow. Use the GetService function to retreive a IDesignerHost reference and use its Container object to add all the workflow activities to the designer surface. See the WorkflowUtils GetAllActivities function for an easy way to get a reference to all nested activities.