sedictor

Немножно переписал:

<?php
class Mongo_LazyLoad {
    private $loaded = false;
    private $mongo;
    private $args;

    public function __construct() {
        $this->args = func_get_args();
    }
    private function init() {
        if (!$this->loaded) {
            $t = create_function(null, 'new Mongo('. implode(',', $this->args) .');');
            $this->mongo = $t();
            $this->loaded = true;
        }
    }
    public function __call($name, array $arguments) {
        $this->init();
        return call_user_func_array(array($this->mongo, $name), $arguments);
    }
    public static function __callStatic($name, array $arguments) {
        $this->__call($name, $arguments);
    }
    public function __get($name) {
        $this->init();
        return $this->mongo->$name;
    }
    public function __set($name, $value) {
        $this->init();
        return $this->mongo->$name = $value;
    }
    public function __isset($name) {
        $this->init();
        return isset($this->mongo->$name);
    }
    public function __unset($name) {
        $this->init();
        unset($this->mongo->$name);
    }
}

И остается заменить new Mongo на new Mongo_LazyLoad.
Этот способ больше подходит для того, чтобы в уже существующем проекте внести минимум изменений

class lazyLoad_mongo {
    private $loaded = false;
    private $mongo;
    public function init() {
        $this->mongo = new Mongo(MONGO_SERVER, array ("connect" => false));
        $this->loaded = true;
    }
    public function __call($name, array $arguments) {
        if (!$this->loaded) {
            $this->init();
        }
        return call_user_func_array(array($this->mongo, $name), $arguments);
    }
    public function __callStatic($name, array $arguments) {
        $this->__call($name, $arguments);
    }
    public function __get($name) {
        if (!$this->loaded) {
            $this->init();
        }
        return $this->mongo->$name;
    }
    public function __set($name, $value) {
        if (!$this->loaded) {
            $this->init();
        }
        return $this->mongo->$name = $value;
    }
    public function __isset($name) {
        if (!$this->loaded) {
            $this->init();
        }
        return isset($this->mongo->$name);
    }
    public function __unset($name) {
        if (!$this->loaded) {
            $this->init();
        }
        return unset($this->mongo->$name);
    }
}