You can link the box to the main view, then pre multiply the link with a translation to keep the box in your view. To keep it from being occluded, you can disable depth test and give it a high draw order.
Code:
box = vizshape.addBox()
link = viz.link( viz.MainView, box )
link.preTrans([0,0,3])
box.disable( viz.DEPTH_TEST )
box.drawOrder(100)
Masaki