Another option is to use a GlassPane
and "grey out" an area of components. You would also have to capture and ignore clicks in the pane for the area you don't want a users clicking.
See more with an example in the Java Tutorial here: http://docs.oracle.com/javase/tutorial/uiswing/components/rootpane.html
This write up could also be helpful: https://weblogs.java.net/blog/alexfromsun/archive/2006/09/a_wellbehaved_g.html