Another way to do it. Using this one into a shelf Button allow you to go between back and front at every hit of the button.
//name of camera
string $frontCam = "front";
string $backCam = "back";
//name of your display layer
string $frontLayer = "frontLayer";
string $backLayer = "backLayer";
//get camera front current view
string $curPan = getPanel -wf;
string $curCam = modelPanel -q -cam $curPan;
//set layer visibility
if($curCam == "back")
{
lookThroughModelPanel $frontCam $curPan;
setAttr ($frontLayer + ".v") 1;
setAttr ($backLayer + ".v") 0;
}
else
{
lookThroughModelPanel $backCam $curPan;
setAttr ($frontLayer + ".v") 0;
setAttr ($backLayer + ".v") 1;
}