How do I turn off a custom IValueConverter at design time? Basically I want to write this:

Public Class MethodBinder
    Implements IValueConverter

    Public Function Convert(ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As CultureInfo) As Object Implements IValueConverter.Convert
        If [DESIGN_TIME] Then Return Nothing
        If value IsNot Nothing Then Return CallByName(value, CStr(parameter), CallType.Method)
        Return Nothing
    End Function

    Public Function ConvertBack(ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As CultureInfo) As Object Implements IValueConverter.ConvertBack
        Throw New NotSupportedException
    End Function
End Class