C# 访问；TaskbarIcon“；从ViewModel查看

我有一个视图，叫做MyView，看起来像这样

<Grid>
    <tb:TaskbarIcon x:Name="MyTaskBar"
                    IconSource="/Icons/Icon.ico"
                    MenuActivation="LeftOrRightClick">

        <tb:TaskbarIcon.ContextMenu>
            <ContextMenu>
                <MenuItem Header="About" cal:Message.Attach="About">
                </MenuItem>
            </ContextMenu>
        </tb:TaskbarIcon.ContextMenu>

    </tb:TaskbarIcon>
</Grid>

如何访问MyViewModel中的“MyTaskBar”？我用的是Caliburn

var myBalloon = new MyBalloonView();
MyTaskBar.ShowCustomBalloon(myBalloon, PopupAnimation.Slide, 100);