This Rhino Script allows the user to select a piece of geometry then selects the inverse and hides it.  Use _show to reveal this geometry.

Rhino Script

Option Explicit 
'Script written by <David Mans> 
'Script copyrighted by <Neoarchaic Studio> 
'Script version Friday, January 16, 2009 9:54:03 PM 
Call Main() 
Sub Main() 
    Dim arrObjects 
    arrObjects = Rhino.getobjects("Select Objects to Isolate",,, True) 
    If isNull(arrObjects) Then Exit Sub
    Call Rhino.EnableRedraw(False) 
    Call Rhino.SelectObjects(arrObjects) 
    Call Rhino.InvertSelectedObjects() 
    Call Rhino.Command("Hide", False) 
    Call Rhino.EnableRedraw(True) 
End Sub