Hey Fred, There are two different VI Server properties that I think may be useful to you. If you haven't used VI Server before here's a link to some general information on it. <a href = http://zone.ni.com/devzone/learningcenter.nsf/03f7c60f17aad210862567a90054a26c/371c4fea97121ea686256c4e0062de8a?OpenDocument>Programmatically Controlling LabVIEW</a> VI Server basically allows you to programmatically control a VI.
One property that may be helpful to you is the Execution:Show Front Panel On Call Property. This property will allow you from your main VI to control whether a subVI's front panel is shown when it's called. Another property is the Front Panel Window:State Property. This property determines the state of the front panel of a VI. For example, you can make the front panel of a VI hidden. Please refer to the help for these properties for more information about them. I hope this helps! Sarah Miracle National Instruments
