Sorry, I don't understand exactly what you're trying to do. You can clone the model to conserve memory:
Code:
import viz
viz.go()
viz.MainWindow.setSize([0.5,1])
subWindow = viz.addWindow(pos=[0.5,1.0])
subWindow.setSize([0.5,1])
dojo = viz.addChild('dojo.osgb')
ball = viz.addChild('beachball.osgb',pos=[0,2.5,3])
ball2 = ball.clone(pos=[0,1,3])
ball.renderOnlyToWindows([viz.MainWindow])
ball2.renderOnlyToWindows([subWindow])