You can do this using custom shapes or map backgrounds images. The shape method is more "stable" at the moment, but you're limited to small sizes (shapes don't scale up that well, the image degrades). The map method can display full, quality images, but there's currently a bug with sizing the image and it can produces deformed images.
I've attach a file that demonstrates how to do the shape method. Here' a link to the map background image method. Good luck.
Images in Table.twbx.zip 480.4 KB