I have never done this so hopefully somebody will give you a better suggestion but Display2d (and cognates) is a JComponent so you should be able to attach the portrayal to the display2d, feed a BufferedImage's graphics object to the display2d paint(g) method and get a fixed image out of it. Something like this:
http://stackoverflow.com/questions/1349220/convert-jpanel-to-imageYou'd probably have to listen to resize events to redraw the image and so on, but it may be what you are looking for.
Portrayals have their own draw(g,x,y) method so there might be a faster, direct way of painting images from them but I am not really sure what the DrawInfo2D argument would look like.
Good luck.