Gerald,
a very simple way of doing so would be to place the whole Manipulate[] in a new extra notebook, i.e.:
CreateDocument[Manipulate[t,
   Control[{{ lt, -20, "Start Temperature", ImageSize -> Tiny}, -40.0,
      240.0, 10.0, ImageSize -> Tiny, Appearance -> "Labeled", 
     ControlPlacement -> Left}],
   Control[{{ incr, 10, "Temp Increment", ImageSize -> Tiny}, 1, 50.0,
      10.0, ImageSize -> Tiny, Appearance -> "Labeled", 
     ControlPlacement -> Left}],
   Control[{{ ut, 120, "End Temp.", ImageSize -> Tiny}, -40.0, 240.0, 
     10.0, ImageSize -> Tiny, Appearance -> "Labeled", 
     ControlPlacement -> Left}],
   Control@{{t, {}, ""},Table[loadcase -> ToString[loadcase] <> " deg C", {loadcase, lt, ut, 
       incr}], ControlType -> CheckboxBar, Appearance -> ("Vertical"),
      ControlPlacement -> Bottom, Appearance -> "Labeled"}], 
    WindowTitle -> "Please Input Values", WindowSize -> All];
Does that fit your needs? Regards -- Henrik