Try this one, it should do the trick.

Copy past to your MEL editor middel drag to your shelf.

string $sel[];
int $temp[];
int $value;

$sel = `ls -sl -dag -ap -typ surfaceShape`;

for ($obj in $sel){
$temp = `displaySurface -q -xRay $obj`;
$value = $temp[0];
if ($value == 1)
displaySurface -xRay 0 $obj;
else
displaySurface -xRay 1 $obj;
}