Use LESS in a live WordPress theme.

filter-stylesheet-uri.php

<?php

if ( ! function_exists( 'less_filter_stylesheet_uri' ) ) {
	function less_filter_stylesheet_uri( $stylesheet_uri, $stylesheet_dir_uri ) {
		$current_user = wp_get_current_user();
		
		if ( $current_user->ID == '1' )
			$src = $stylesheet_dir_uri . '/style.less';
		else
			$src = $stylesheet_dir_uri . '/style.min.css';
		
		return $src;
	}
	add_filter( 'stylesheet_uri', 'less_filter_stylesheet_uri', 10, 2 );
}

less-add-theme-stylesheet.php

<?php

if ( ! function_exists( 'less_add_theme_stylesheet' ) ) {
	function less_add_theme_stylesheet() {
		$current_user = wp_get_current_user();
	
		if ( ! builder_disable_theme_stylesheets() ) {
			if ( $current_user->ID == '1' )
				echo '<link rel="stylesheet/less" href="' . get_stylesheet_uri() . '" type="text/css" media="screen" />' . "\n";
			else
				echo '<link rel="stylesheet" href="' . get_stylesheet_uri() . '" type="text/css" media="screen" />' . "\n";
		}
	}
	add_action( 'builder_add_stylesheets', 'less_add_theme_stylesheet', 0 );
}

less-enqueue-script.php

<?php

if ( ! function_exists( 'less_enqueue_scripts' ) ) {
	function less_enqueue_scripts() {
		
		$current_user = wp_get_current_user();
		
		/**
		 * Let's enqueue less to use in the for me
		 * only. That is user ID 1 or user kopepasah.
		*/
		if ( $current_user->ID == '1' )
			wp_enqueue_script( 'lesscss', get_stylesheet_directory_uri() . '/js/less.min.js' );
		
	}
	add_action( 'wp_enqueue_scripts', 'less_enqueue_scripts' );
}

less-remove-stylesheets.php

<?php

if ( ! function_exists( 'less_remove_stylesheets' ) ) {
	function less_remove_stylesheets() {
		remove_action( 'builder_add_stylesheets', 'builder_add_theme_stylesheet', 0 );
	}
	add_action( 'init', 'less_remove_stylesheets' );
}

lessc.sh

lessc --yui-compress style.less > style.min.css

standard-theme-header.php

<?php

$current_user = wp_get_current_user();
	
if ( $current_user->ID == '1' )
	echo '<link rel="stylesheet/less" href="' . get_stylesheet_uri() . '" type="text/css" media="screen" />' . "\n";
else
	echo '<link rel="stylesheet" href="' . get_stylesheet_uri() . '" type="text/css" media="screen" />' . "\n";