An old post so excuse the late response.
Instead of using the designer to place your bits perhaps use photoshop, elements or Gimp. Photoshop is a great tool for being able to zoom in/out of a design. Each element of the design is a separate layer. There are a couple of photoshop scripts that convert the design into yahoo or QT widget XML and separate the graphical elements out into distinct images.
When this conversion is complete you can drop the components onto the Xwidget Designer or simply convert the foreign widget XML to Xwidget's particular form.
I created a guide to the above here: http://lightquick.co.uk/how-to-create-a-yahoo-widget.html?Itemid=252
It forms the first stage of any of my widgets regardless of the final engine I am porting to.