如何在多绑定中为一个绑定传递一个常量值?

I have a multi-binding like

我有一个多绑定的

<TextBlock>
    <TextBlock.Text>
        <MultiBinding Converter="{StaticResource myConverter}">
            <Binding Path="myFirst.Value" />
            <Binding Path="mySecond.Value" />
        </MultiBinding>
    </TextBlock.Text>
</TextBlock>
<TextB