In theory it is possible but will depend on how will Java Print services supports your printer. The print property javax.print.attribute.standard.MediaTray can be added to the PrintHelper HashDocAttributeSet docAttributeSet isntance variable at construction time or via the setupPrinterServices call. The MediaTray attribute is mentioned here, http://java.sun.com/j2se/1.5.0/docs/guide/jps/spec/JPSTOC.fm.html
The example application ./printservices/PrintServices.java can be used to test the supported job properties for the selected printer. This might be a good test for you to see if your printer supports tray selection.
I had found that but looking at the Javadoc it suggests it is for input trays, not output trays. The static options on it are for choosing the envelope trays or manual feed etc.