Warren,
I am assuming that you want to do this during edit mode, which I don't believe you can.
However, you could write a VI to do it using VI server. You can open a reference to the main VI and then use the callees property to get the names of the SubVIs, there is also a property Execution>>Show Front Panel on Call. You may have to then open references to the SubVIs, and continue the process until you have found all the VIs, and whether they are set to show on front panel.