Here's xray shader mel script from digital tutors I think..

// ----------
// dlXray.mel
// ----------
// DATE:	05/24/2003, rev. 06/17/2003
//
// AUTHOR:	David LeFebvre
//
// COMPANY:     PL Studios, Inc.  Digital-Tutors.com
//
// DESCRIPTION:	This script will toggle the x-ray display of the shape
//		nodes for all selected surfaces.
// USAGE:	select one or more surfaces, execute the procedure
//
// EXAMPLE:	select -r spere1; dlXray;
//
// DISCLAIMER:  Use this an all scripts at your own risk.  PL Studios,
Inc. will not be responsible
//              for any data loss or file corruption from the use of this
script.

global proc dlXray (){

// declare variables
string $selected[];
string $hilited[];
string $object;
int $test[];
int $hold;

	// assign values to variables for selected objects
	$selected = `ls -sl -dag -ap -typ surfaceShape`;
	$hilited = `ls -hl -dag -ap -typ surfaceShape`;

	// loop through any objects in component mode
	// and toggle their x-ray display
	for ($object in $hilited){
		$test = `displaySurface -q -xRay $object`;
		$hold = $test[0];
		if ($hold != false)
		  displaySurface -xRay false $object;
		else
		  displaySurface -xRay true $object;

		// clear test variable
		clear $test;
	}

	// loop through any objects in object mode
	// and toggle their x-ray display
	for ($object in $selected){
		$test = `displaySurface -q -xRay $object`;
		$hold = $test[0];
		if ($hold != false)
		  displaySurface -xRay false $object;
		else
		  displaySurface -xRay true $object;

		// clear test variable
		clear $test;
	}
	
	// clear selection variables
	clear $selected;
	clear $hilited;