Allow WPF Grid cell content to expand outside of the grid cell?

I have a Grid in my WPF window. When a particular button is pressed, I want a control in one of the Grid cells to expand downward to double its original size. When this happens, the control is clipped to the visual bounds of the containing cell. However, I need all of the content to be visible, over the top of the cell below. I tried setting Panel.ZIndex to a high value, to no avail. I basically need to emulate the functionality of "overflow:visible" in CSS. Is this possible in WPF/Xaml?