If my thoughts are correct. You want to include methods from another model into a seperate model...

In this case, you can use the __construct method in your model that is extending the external class:

   private $external;

    public function __construct(ExternalClass $external)
    {
        $this->external = $external;
    }

then, in other methods in the class that is extending the ExternalClass, you can call the method with:

    public function thingDoer() 
    {
        return $this->external->thingThatDoes();
    }

Code not tested so let me know if this helps!

Edit: I think in php5.4+ you may need to use:

class Model extends Eloquent {

    use External;

    public function thingDoer() 
    {
        return $this->thingThatDoes();
    }
}

class External {
     public function thingThatDoes(){ return $something };
}

There are a few ways to do this, but it depends on how your personal project is structured. Try to stay consistent with your practices.