I am sorry for not being clear.. in fact my answer was misleading. Closing a front-panel (as previously described) is NOT the same as making the front-panel invisible. You instead will want to set state of the front-panel to "hidden" using the FP.state property.
To get back the panel (make it visible), you will write "standard" to the FP.state.
See the following example (in your LabVIEW) folder for how to do this: \examples\viserver\FrontPanelStates.vi
Khalid