在我与RibbonWindow一点经验，我看到丝带是ribbonwindow本身的内容的一部分。所以，解决办法是公开为设置你的用户控件，这样的功能区窗口的公共方法：

In my little experience with RibbonWindow, i saw that ribbon is part of the content of the ribbonwindow itself. So, a solution could be to expose a public method for the ribbon window that set your usercontrol, like this:

<ribbon:RibbonWindow ...>
<Grid x:Name="LayoutRoot">
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>

    <ribbon:Ribbon x:Name="Ribbon" />
    //add a container for your usercontrol
    <Grid Name="contentPlaceHolder" Grid.Row="1"></Grid>   
 </Grid>

和代码，你可以设置像

public void SetControl(UserControl uc)
{
   this.contentPlaceHolder.Content = uc; 
}