仅调整WPF中用户控件的剪切区域的大小

I have a predefined User Control from a third party library. I would like to cut off a region from this User Control and use it in the Main window. Clipping is easily done with the Clip property of a UIElement but then the resizing does not work for this single segment. Is it possible to cut from a UIElement or User Control and use only this region for measuring, resizing and rendering of the component? I have a predefined User Control from a third p